cygwin vfork

cygwin vfork

[Charles Wilson]

Seen on the XEmacs list:

 > In general the cygwin build is slower, I think this is for 3 main
 > reasons:
 >
 > 1) gcc optimization is not as good as MSVC
 > 2) The cygwin portability layer adds a lot of overhead especially
 > wrt file handling.
 > 3) The cygwin implementation of fork-and-exec doesn't jive well with
 > the VM size of xemacs. Supposedly a real vfork is in the works for
 > cygwin but I can't attest to its functionality.

Does #3 make any sense?  I thought we *had* a real vfork...perhaps it 
doesn't work well with large apps?  Or is the author just blowing smoke?

--Chuck


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Re: cygwin vfork

[Christopher Faylor]

On Mon, Nov 12, 2001 at 01:45:01PM -0500, Charles Wilson wrote:
>Seen on the XEmacs list:
>
>> In general the cygwin build is slower, I think this is for 3 main
>> reasons:
>>
>> 1) gcc optimization is not as good as MSVC
>> 2) The cygwin portability layer adds a lot of overhead especially
>> wrt file handling.
>> 3) The cygwin implementation of fork-and-exec doesn't jive well with
>> the VM size of xemacs. Supposedly a real vfork is in the works for
>> cygwin but I can't attest to its functionality.
>
>Does #3 make any sense?  I thought we *had* a real vfork...perhaps it 
>doesn't work well with large apps?  Or is the author just blowing smoke?

We have had a sort-of-vfork that should be faster than fork since 1.3.3,
I think.  No idea what the VM goobledy-gook is referring to.

Cygwin's vfork is just black magic that eventually results in running
spawn(P_NOWAIT) rather than fork/exec.

cgf

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Re: cygwin vfork

[Tim Prince]

----- Original Message -----
From: "Charles Wilson" <cwilson@ece.gatech.edu>
To: <cygwin@cygwin.com>
Sent: Monday, November 12, 2001 10:45 AM
Subject: cygwin vfork


> Seen on the XEmacs list:
>
>  > In general the cygwin build is slower, I think this is for 3 main
>  > reasons:
>  >
>  > 1) gcc optimization is not as good as MSVC
>  > 2) The cygwin portability layer adds a lot of overhead especially
>  > wrt file handling.
>  > 3) The cygwin implementation of fork-and-exec doesn't jive well with
>  > the VM size of xemacs. Supposedly a real vfork is in the works for
>  > cygwin but I can't attest to its functionality.
>
> Does #3 make any sense?  I thought we *had* a real vfork...perhaps it
> doesn't work well with large apps?  Or is the author just blowing smoke?
>
> --Chuck
>
#1 doesn't make a great deal of sense either.  I suppose it's possible to
set up ground rules under which MSVC would optimize better than gcc, but
it's not my experience.


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AW: cygwin vfork

[Ralf Habacker]

>
> Seen on the XEmacs list:
>
>  > In general the cygwin build is slower, I think this is for 3 main
>  > reasons:
>  >
>  > 1) gcc optimization is not as good as MSVC
>  > 2) The cygwin portability layer adds a lot of overhead especially
>  > wrt file handling.
>  > 3) The cygwin implementation of fork-and-exec doesn't jive well with
>  > the VM size of xemacs. Supposedly a real vfork is in the works for
>  > cygwin but I can't attest to its functionality.
>
> Does #3 make any sense?  I thought we *had* a real vfork...perhaps it
> doesn't work well with large apps?
>
Can you explain this a little bit more ? I'm asking because in
http://sources.redhat.com/ml/cygwin-xfree/2001-q4/msg00276.html I have described
some problems with kde2 on cygwin relating performance and I'm very interested
in getting more informations how to fix these problems. In short, loading the
full kde2 desktop needs about 4 minutes and the reaction time for starting apps
are  > 1 minute. This seems to be unusable.
My assumption are that these problems depends on application loading (vfork is
used on every app), file and socket io.
A regular kde2 app uses about 20-40 dll's, so a faster vfork would decrease the
loading time. :-)

Regards
Ralf

> --Chuck
>
>
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Re: AW: cygwin vfork

[Charles Wilson]

Ralf Habacker wrote:

>> > 3) The cygwin implementation of fork-and-exec doesn't jive well with
>> > the VM size of xemacs. Supposedly a real vfork is in the works for
>> > cygwin but I can't attest to its functionality.


> Can you explain this a little bit more ? I'm asking because in
> http://sources.redhat.com/ml/cygwin-xfree/2001-q4/msg00276.html I have described
> some problems with kde2 on cygwin relating performance and I'm very interested
> in getting more informations how to fix these problems. In short, loading the
> full kde2 desktop needs about 4 minutes and the reaction time for starting apps
> are  > 1 minute. This seems to be unusable.
> My assumption are that these problems depends on application loading (vfork is
> used on every app), file and socket io.
> A regular kde2 app uses about 20-40 dll's, so a faster vfork would decrease the
> loading time. :-)


Well, this is the clarification that I received:

 > The VM comment is referring to the large footprint of XEmacs which means
 > that doing a fork requires copying an awful lot of data (and hence takes a
 > long time), most OS's do copy-on-write for vfork so the overhead is never
 > incurred.

And of course, cgf chimed in on this thread, but I can't find his message 
in my mail archive, and (as mentioned elsewhere) the cygwin ml archive is 
missing his message as well, so I can't quote it here for you.

--Chuck




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Re: AW: cygwin vfork

[Christopher Faylor]

On Tue, Nov 13, 2001 at 10:43:03AM -0500, Charles Wilson wrote:
>> The VM comment is referring to the large footprint of XEmacs which means
>> that doing a fork requires copying an awful lot of data (and hence takes a
>> long time), most OS's do copy-on-write for vfork so the overhead is never
>> incurred.
>
>And of course, cgf chimed in on this thread, but I can't find his message 
>in my mail archive, and (as mentioned elsewhere) the cygwin ml archive is 
>missing his message as well, so I can't quote it here for you.

With vfork, there is very little copying going on.  Only cygwin's heap is
copied.

Of course, if you don't use vfork then cygwin's fork implementation *is*
pretty slow.

cgf

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Re: cygwin vfork

[Christopher Faylor]

On Tue, Nov 13, 2001 at 12:48:24PM +0100, Ralf Habacker wrote:
>>
>> Seen on the XEmacs list:
>>
>>  > In general the cygwin build is slower, I think this is for 3 main
>>  > reasons:
>>  >
>>  > 1) gcc optimization is not as good as MSVC
>>  > 2) The cygwin portability layer adds a lot of overhead especially
>>  > wrt file handling.
>>  > 3) The cygwin implementation of fork-and-exec doesn't jive well with
>>  > the VM size of xemacs. Supposedly a real vfork is in the works for
>>  > cygwin but I can't attest to its functionality.
>>
>> Does #3 make any sense?  I thought we *had* a real vfork...perhaps it
>> doesn't work well with large apps?
>>
>Can you explain this a little bit more ? I'm asking because in
>http://sources.redhat.com/ml/cygwin-xfree/2001-q4/msg00276.html I have described
>some problems with kde2 on cygwin relating performance and I'm very interested
>in getting more informations how to fix these problems. In short, loading the
>full kde2 desktop needs about 4 minutes and the reaction time for starting apps
>are  > 1 minute. This seems to be unusable.
>My assumption are that these problems depends on application loading (vfork is
>used on every app), file and socket io.

You can't make an assumption like this.  It's possible that there is
something in your app which is short-circuiting cygwin's vfork.  There
are some pathological cases in which it will give up and revert to fork.

It's unlikely that gcc's optimization is so very bad that you'd see orders
of magnitude slowdowns.  So, something else is going on.  You'd have to
debug the application to figure out what that is.

cgf

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Re: cygwin vfork

[Christopher Faylor]

On Mon, Nov 12, 2001 at 01:45:01PM -0500, Charles Wilson wrote:
>Seen on the XEmacs list:
>
>> In general the cygwin build is slower, I think this is for 3 main
>> reasons:
>>
>> 1) gcc optimization is not as good as MSVC
>> 2) The cygwin portability layer adds a lot of overhead especially
>> wrt file handling.
>> 3) The cygwin implementation of fork-and-exec doesn't jive well with
>> the VM size of xemacs. Supposedly a real vfork is in the works for
>> cygwin but I can't attest to its functionality.
>
>Does #3 make any sense?  I thought we *had* a real vfork...perhaps it 
>doesn't work well with large apps?  Or is the author just blowing smoke?

We have had a sort-of-vfork that should be faster than fork since 1.3.3,
I think.  No idea what the VM goobledy-gook is referring to.

Cygwin's vfork is just black magic that eventually results in running
spawn(P_NOWAIT) rather than fork/exec.

cgf

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AW: cygwin vfork

[Ralf Habacker]

>
> Seen on the XEmacs list:
>
>  > In general the cygwin build is slower, I think this is for 3 main
>  > reasons:
>  >
>  > 1) gcc optimization is not as good as MSVC
>  > 2) The cygwin portability layer adds a lot of overhead especially
>  > wrt file handling.
>  > 3) The cygwin implementation of fork-and-exec doesn't jive well with
>  > the VM size of xemacs. Supposedly a real vfork is in the works for
>  > cygwin but I can't attest to its functionality.
>
> Does #3 make any sense?  I thought we *had* a real vfork...perhaps it
> doesn't work well with large apps?
>
Can you explain this a little bit more ? I'm asking because in
http://sources.redhat.com/ml/cygwin-xfree/2001-q4/msg00276.html I have described
some problems with kde2 on cygwin relating performance and I'm very interested
in getting more informations how to fix these problems. In short, loading the
full kde2 desktop needs about 4 minutes and the reaction time for starting apps
are  > 1 minute. This seems to be unusable.
My assumption are that these problems depends on application loading (vfork is
used on every app), file and socket io.
A regular kde2 app uses about 20-40 dll's, so a faster vfork would decrease the
loading time. :-)

Regards
Ralf

> --Chuck
>
>
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cygwin vfork

[Charles Wilson]

Seen on the XEmacs list:

 > In general the cygwin build is slower, I think this is for 3 main
 > reasons:
 >
 > 1) gcc optimization is not as good as MSVC
 > 2) The cygwin portability layer adds a lot of overhead especially
 > wrt file handling.
 > 3) The cygwin implementation of fork-and-exec doesn't jive well with
 > the VM size of xemacs. Supposedly a real vfork is in the works for
 > cygwin but I can't attest to its functionality.

Does #3 make any sense?  I thought we *had* a real vfork...perhaps it 
doesn't work well with large apps?  Or is the author just blowing smoke?

--Chuck


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Re: cygwin vfork

[Tim Prince]

----- Original Message -----
From: "Charles Wilson" <cwilson@ece.gatech.edu>
To: <cygwin@cygwin.com>
Sent: Monday, November 12, 2001 10:45 AM
Subject: cygwin vfork


> Seen on the XEmacs list:
>
>  > In general the cygwin build is slower, I think this is for 3 main
>  > reasons:
>  >
>  > 1) gcc optimization is not as good as MSVC
>  > 2) The cygwin portability layer adds a lot of overhead especially
>  > wrt file handling.
>  > 3) The cygwin implementation of fork-and-exec doesn't jive well with
>  > the VM size of xemacs. Supposedly a real vfork is in the works for
>  > cygwin but I can't attest to its functionality.
>
> Does #3 make any sense?  I thought we *had* a real vfork...perhaps it
> doesn't work well with large apps?  Or is the author just blowing smoke?
>
> --Chuck
>
#1 doesn't make a great deal of sense either.  I suppose it's possible to
set up ground rules under which MSVC would optimize better than gcc, but
it's not my experience.


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AW: cygwin vfork

[Ralf Habacker]

[-- Attachment #1: Type: text/plain, Size: 5310 bytes --]

> -----Ursprüngliche Nachricht-----
> Von: cygwin-owner@sources.redhat.com
> [mailto:cygwin-owner@sources.redhat.com]Im Auftrag von Ralf Habacker
> Gesendet am: Mittwoch, 14. November 2001 16:22
> An: cygwin@cygwin.com
> Betreff: AW: cygwin vfork
>
> > -----Ursprüngliche Nachricht-----
> > Von: cygwin-owner@sources.redhat.com
> > [mailto:cygwin-owner@sources.redhat.com]Im Auftrag von Christopher
> > Faylor
> > Gesendet am: Dienstag, 13. November 2001 19:15
> > An: cygwin@cygwin.com
> > Betreff: Re: cygwin vfork
> >
> > On Tue, Nov 13, 2001 at 12:48:24PM +0100, Ralf Habacker wrote:
> > >>
> > >> Seen on the XEmacs list:
> > >>
> > >>  > In general the cygwin build is slower, I think this is for 3 main
> > >>  > reasons:
> > >>  >
> > >>  > 1) gcc optimization is not as good as MSVC
> > >>  > 2) The cygwin portability layer adds a lot of overhead especially
> > >>  > wrt file handling.
> > >>  > 3) The cygwin implementation of fork-and-exec doesn't jive well with
> > >>  > the VM size of xemacs. Supposedly a real vfork is in the works for
> > >>  > cygwin but I can't attest to its functionality.
> > >>
> > >> Does #3 make any sense?  I thought we *had* a real vfork...perhaps it
> > >> doesn't work well with large apps?
> > >>
> > >Can you explain this a little bit more ? I'm asking because in
> > >http://sources.redhat.com/ml/cygwin-xfree/2001-q4/msg00276.html I
> > have described
> > >some problems with kde2 on cygwin relating performance and I'm very
> > interested
> > >in getting more informations how to fix these problems. In short,
> loading the
> > >full kde2 desktop needs about 4 minutes and the reaction time for
> > starting apps
> > >are  > 1 minute. This seems to be unusable.
> > >My assumption are that these problems depends on application loading
> > (vfork is
> > >used on every app), file and socket io.
> >
> > You can't make an assumption like this.  It's possible that there is
> > something in your app which is short-circuiting cygwin's vfork.  There
> > are some pathological cases in which it will give up and revert to fork.
>
> Hmmh, it may be that vfork in the closest context would not be a problem, but
> remember the problem in dll_list::alloc
> http://sources.redhat.com/ml/cygwin-xfree/2001-q4/msg00295.html where
> I have to
> increase the number of retries on searching a free memory area.
> I recognized, that there are sometimes over 150 tries needed to find a free
> block and when an application uses 40 dll's, this produces some overhead.
> Additional the performance of the windows run time loader seems to not be the
> best, especially when using c++ dll's with many symbols.
> There may be some more aspects I currently can't identify, and you're right,
> this has to be debugged.
>
> A few weeks ago I have build a debug release of the cygwin dll with printing
> some debug information in the dll loading stuff and recognized, that there are
> noticable delays on application loading.
>
> Second file and socket communication seems to be parts, which has to be
> observed. I have build a file io test app using fopen/fread/fwrite, which
> compares file io with cygwin and mscrt and this reports in some cases
> that file
> io with cygwin needs about than 10 times as much as with msvcrt to read/write
> files. In the next time I'm analysing this a little bit more.
>
Here are some results of the file io test program, which is appended. Note the
differences in the read case

$ make check
fileio_cyg      no operation check      count=100                       0:00.08s
real,  0.04s user,     0.05s sys
fileio_ms.exe   no operation check      count=100                       0:00.08s
real,  0.03s user,     0.05s sys
fileio_cyg      file open check         count=100                       0:00.16s
real,  0.07s user,     0.10s sys
fileio_ms.exe   file open check         count=100                       0:00.11s
real,  0.05s user,     0.03s sys
fileio_cyg      file write check        count=100       size=   65536   0:01.72s
real,  0.10s user,     0.51s sys
fileio_ms.exe   file write check        count=100       size=   65536   0:01.29s
real,  0.04s user,     0.04s sys

fileio_cyg      file read check         count=100       size=   65536   0:01.06s
real,  0.09s user,     0.12s sys
fileio_ms.exe   file read check         count=100       size=   65536   0:00.12s
real,  0.02s user,     0.06s sys

^^^^^^^^^^
fileio_cyg      file write check        count=100       size=  131072   0:11.98s
real,  0.09s user,     0.73s sys
fileio_ms.exe   file write check        count=100       size=  131072   0:08.13s
real,  0.03s user,     0.03s sys

fileio_cyg      file read check         count=100       size=  131072   0:02.33s
real,  0.14s user,     0.12s sys
fileio_ms.exe   file read check         count=100       size=  131072   0:00.14s
real,  0.03s user,     0.04s sys
                                                                        ^^^^^^^^
fileio_cyg      file write check        count= 10       size= 1048576   0:08.70s
real,  0.06s user,     0.52s sys
fileio_ms.exe   file write check        count= 10       size= 1048576   0:04.53s
real,  0.05s user,     0.03s sys

It seems that the msvc runtime does a more efficient read caching as cygwin.
Does anyone have some suggestions about the possible reason why ?

Regards

 Ralf

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Re: AW: cygwin vfork

[Christopher Faylor]

On Tue, Nov 13, 2001 at 10:43:03AM -0500, Charles Wilson wrote:
>> The VM comment is referring to the large footprint of XEmacs which means
>> that doing a fork requires copying an awful lot of data (and hence takes a
>> long time), most OS's do copy-on-write for vfork so the overhead is never
>> incurred.
>
>And of course, cgf chimed in on this thread, but I can't find his message 
>in my mail archive, and (as mentioned elsewhere) the cygwin ml archive is 
>missing his message as well, so I can't quote it here for you.

With vfork, there is very little copying going on.  Only cygwin's heap is
copied.

Of course, if you don't use vfork then cygwin's fork implementation *is*
pretty slow.

cgf

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Re: AW: cygwin vfork

[Charles Wilson]

Ralf Habacker wrote:

>> > 3) The cygwin implementation of fork-and-exec doesn't jive well with
>> > the VM size of xemacs. Supposedly a real vfork is in the works for
>> > cygwin but I can't attest to its functionality.


> Can you explain this a little bit more ? I'm asking because in
> http://sources.redhat.com/ml/cygwin-xfree/2001-q4/msg00276.html I have described
> some problems with kde2 on cygwin relating performance and I'm very interested
> in getting more informations how to fix these problems. In short, loading the
> full kde2 desktop needs about 4 minutes and the reaction time for starting apps
> are  > 1 minute. This seems to be unusable.
> My assumption are that these problems depends on application loading (vfork is
> used on every app), file and socket io.
> A regular kde2 app uses about 20-40 dll's, so a faster vfork would decrease the
> loading time. :-)


Well, this is the clarification that I received:

 > The VM comment is referring to the large footprint of XEmacs which means
 > that doing a fork requires copying an awful lot of data (and hence takes a
 > long time), most OS's do copy-on-write for vfork so the overhead is never
 > incurred.

And of course, cgf chimed in on this thread, but I can't find his message 
in my mail archive, and (as mentioned elsewhere) the cygwin ml archive is 
missing his message as well, so I can't quote it here for you.

--Chuck




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Re: cygwin vfork

[Christopher Faylor]

On Tue, Nov 13, 2001 at 12:48:24PM +0100, Ralf Habacker wrote:
>>
>> Seen on the XEmacs list:
>>
>>  > In general the cygwin build is slower, I think this is for 3 main
>>  > reasons:
>>  >
>>  > 1) gcc optimization is not as good as MSVC
>>  > 2) The cygwin portability layer adds a lot of overhead especially
>>  > wrt file handling.
>>  > 3) The cygwin implementation of fork-and-exec doesn't jive well with
>>  > the VM size of xemacs. Supposedly a real vfork is in the works for
>>  > cygwin but I can't attest to its functionality.
>>
>> Does #3 make any sense?  I thought we *had* a real vfork...perhaps it
>> doesn't work well with large apps?
>>
>Can you explain this a little bit more ? I'm asking because in
>http://sources.redhat.com/ml/cygwin-xfree/2001-q4/msg00276.html I have described
>some problems with kde2 on cygwin relating performance and I'm very interested
>in getting more informations how to fix these problems. In short, loading the
>full kde2 desktop needs about 4 minutes and the reaction time for starting apps
>are  > 1 minute. This seems to be unusable.
>My assumption are that these problems depends on application loading (vfork is
>used on every app), file and socket io.

You can't make an assumption like this.  It's possible that there is
something in your app which is short-circuiting cygwin's vfork.  There
are some pathological cases in which it will give up and revert to fork.

It's unlikely that gcc's optimization is so very bad that you'd see orders
of magnitude slowdowns.  So, something else is going on.  You'd have to
debug the application to figure out what that is.

cgf

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AW: cygwin vfork

[Ralf Habacker]

> -----Ursprüngliche Nachricht-----
> Von: cygwin-owner@sources.redhat.com
> [mailto:cygwin-owner@sources.redhat.com]Im Auftrag von Christopher
> Faylor
> Gesendet am: Dienstag, 13. November 2001 19:15
> An: cygwin@cygwin.com
> Betreff: Re: cygwin vfork
>
> On Tue, Nov 13, 2001 at 12:48:24PM +0100, Ralf Habacker wrote:
> >>
> >> Seen on the XEmacs list:
> >>
> >>  > In general the cygwin build is slower, I think this is for 3 main
> >>  > reasons:
> >>  >
> >>  > 1) gcc optimization is not as good as MSVC
> >>  > 2) The cygwin portability layer adds a lot of overhead especially
> >>  > wrt file handling.
> >>  > 3) The cygwin implementation of fork-and-exec doesn't jive well with
> >>  > the VM size of xemacs. Supposedly a real vfork is in the works for
> >>  > cygwin but I can't attest to its functionality.
> >>
> >> Does #3 make any sense?  I thought we *had* a real vfork...perhaps it
> >> doesn't work well with large apps?
> >>
> >Can you explain this a little bit more ? I'm asking because in
> >http://sources.redhat.com/ml/cygwin-xfree/2001-q4/msg00276.html I
> have described
> >some problems with kde2 on cygwin relating performance and I'm very
> interested
> >in getting more informations how to fix these problems. In short, loading the
> >full kde2 desktop needs about 4 minutes and the reaction time for
> starting apps
> >are  > 1 minute. This seems to be unusable.
> >My assumption are that these problems depends on application loading
> (vfork is
> >used on every app), file and socket io.
>
> You can't make an assumption like this.  It's possible that there is
> something in your app which is short-circuiting cygwin's vfork.  There
> are some pathological cases in which it will give up and revert to fork.

Hmmh, it may be that vfork in the closest context would not be a problem, but
remember the problem in dll_list::alloc
http://sources.redhat.com/ml/cygwin-xfree/2001-q4/msg00295.html where I have to
increase the number of retries on searching a free memory area.
I recognized, that there are sometimes over 150 tries needed to find a free
block and when an application uses 40 dll's, this produces some overhead.
Additional the performance of the windows run time loader seems to not be the
best, especially when using c++ dll's with many symbols.
There may be some more aspects I currently can't identify, and you're right,
this has to be debugged.

A few weeks ago I have build a debug release of the cygwin dll with printing
some debug information in the dll loading stuff and recognized, that there are
noticable delays on application loading.

Second file and socket communication seems to be parts, which has to be
observed. I have build a file io test app using fopen/fread/fwrite, which
compares file io with cygwin and mscrt and this reports in some cases that file
io with cygwin needs about than 10 times as much as with msvcrt to read/write
files. In the next time I'm analysing this a little bit more.

Regards

Ralf












> It's unlikely that gcc's optimization is so very bad that you'd see orders
> of magnitude slowdowns.  So, something else is going on.  You'd have to
> debug the application to figure out what that is.
>
> cgf
>
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