From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: linux-kernel@vger.kernel.org, Linus Torvalds <torvalds@osdl.org>,
Andrew Morton <akpm@osdl.org>, Ingo Molnar <mingo@redhat.com>,
Greg Kroah-Hartman <gregkh@suse.de>,
Christoph Hellwig <hch@infradead.org>,
ltt-dev@shafik.org, systemtap@sources.redhat.com,
Douglas Niehaus <niehaus@eecs.ku.edu>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 05/05] Linux Kernel Markers, non optimised architectures
Date: Fri, 12 Jan 2007 05:10:00 -0000 [thread overview]
Message-ID: <45A71827.6020300@yahoo.com.au> (raw)
In-Reply-To: <20070112050032.GA14100@Krystal>
Mathieu Desnoyers wrote:
> * Nick Piggin (nickpiggin@yahoo.com.au) wrote:
>
>>Mathieu Desnoyers wrote:
>>
>>
>>>+#define MARK(name, format, args...) \
>>>+ do { \
>>>+ static marker_probe_func *__mark_call_##name = \
>>>+ __mark_empty_function; \
>>>+ volatile static char __marker_enable_##name = 0; \
>>>+ static const struct __mark_marker_c __mark_c_##name \
>>>+ __attribute__((section(".markers.c"))) = \
>>>+ { #name, &__mark_call_##name, format } ; \
>>>+ static const struct __mark_marker __mark_##name \
>>>+ __attribute__((section(".markers"))) = \
>>>+ { &__mark_c_##name, &__marker_enable_##name } ; \
>>>+ asm volatile ( "" : : "i" (&__mark_##name)); \
>>>+ __mark_check_format(format, ## args); \
>>>+ if (unlikely(__marker_enable_##name)) { \
>>>+ preempt_disable(); \
>>>+ (*__mark_call_##name)(format, ## args); \
>>>+ preempt_enable_no_resched(); \
>>
>>Why not just preempt_enable() here?
>>
>
>
> Because the preempt_enable() macro contains preempt_check_resched(), which
> may call preempt_schedule() which leads us to a call to schedule(). Therefore,
> all those very interesting scheduler functions would cause an infinite
> recursive scheduler call if we marked schedule() and used preempt_enable() in
> the marker.
The vast majority of schedule() has preempt turned off, so that shouldn't
be a problem, if you provide a comment.
> The primary goal for the markers (and the probes that attaches to them) is to
> have the fewest side-effects possible : any kernel method called from an
> instrumentation site adds this precise kernel method to the "cannot be
> instrumented" list, which I want to keep as small possible.
OK, well one problem is that it can cause a resched event to be lost, so
you might say it has more side-effects without checking resched.
--
SUSE Labs, Novell Inc.
Send instant messages to your online friends http://au.messenger.yahoo.com
next prev parent reply other threads:[~2007-01-12 5:10 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-01-12 0:02 [PATCH 00/05] Linux Kernel Markers Mathieu Desnoyers
2007-01-12 0:07 ` [PATCH 02/05] Linux Kernel Markers, architecture independant code Mathieu Desnoyers
2007-01-12 0:07 ` [PATCH 03/05] Linux Kernel Markers : powerpc optimisation Mathieu Desnoyers
2007-01-12 0:12 ` [PATCH 05/05] Linux Kernel Markers, non optimised architectures Mathieu Desnoyers
2007-01-12 4:39 ` Nick Piggin
2007-01-12 5:05 ` Mathieu Desnoyers
2007-01-12 5:10 ` Nick Piggin [this message]
2007-01-12 17:20 ` Mathieu Desnoyers
2007-01-12 17:43 ` Mathieu Desnoyers
2007-01-12 18:23 ` [PATCH 05/05] update - " Mathieu Desnoyers
2007-01-12 0:12 ` [PATCH 01/05] Linux Kernel Markers : Kconfig menus Mathieu Desnoyers
2007-01-12 0:42 ` [PATCH 04/05] Linux Kernel Markers : i386 optimisation Mathieu Desnoyers
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=45A71827.6020300@yahoo.com.au \
--to=nickpiggin@yahoo.com.au \
--cc=akpm@osdl.org \
--cc=gregkh@suse.de \
--cc=hch@infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=ltt-dev@shafik.org \
--cc=mathieu.desnoyers@polymtl.ca \
--cc=mingo@redhat.com \
--cc=niehaus@eecs.ku.edu \
--cc=systemtap@sources.redhat.com \
--cc=tglx@linutronix.de \
--cc=torvalds@osdl.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).