From: David Smith <dsmith@redhat.com>
To: yzhu1 <Yanjun.Zhu@windriver.com>,
sshukla@mvista.com, systemtap@sourceware.org
Subject: Re: [PATCH 1/1] stp: rt: replace spin_lock with stp style lock and use STP_ALLOC_FLAGS
Date: Wed, 18 Nov 2015 17:14:00 -0000 [thread overview]
Message-ID: <564CB1DE.5040708@redhat.com> (raw)
In-Reply-To: <564C337B.7060306@windriver.com>
On 11/18/2015 02:14 AM, yzhu1 wrote:
> Hi, David
>
> Thanks for your comments.
>
> I can not reproduce this problem. And my user can reproduce this problem
> ocassionly.
> And I requested him to help me to make tests about your changes. But he
> refused.
>
> So I made auto tests in systemtap after this patch is applied. And I can
> not find any
> regressions about this patch.
Most of the time you won't see any difference when using STP_ALLOC_FLAGS
in place of STP_ALLOC_SLEEP_FLAGS. You would see a difference if your
system is under memory pressure.
Let me refresh everyone's knowledge of the difference between
STP_ALLOC_FLAGS and STP_ALLOC_SLEEP_FLAGS. When using STP_ALLOC_FLAGS,
if memory isn't available, the allocation will fail. When using
STP_ALLOC_SLEEP_FLAGS, the kernel will try to wait until memory is
available. Obviously, we can only use STP_ALLOC_SLEEP_FLAGS in certain
places in the code where sleeping is permitted.
If changing STP_ALLOC_SLEEP_FLAGS to STP_ALLOC_FLAGS makes a difference,
this really means that we're using STP_ALLOC_SLEEP_FLAGS in a place
where it isn't safe to sleep.
It could be that in the normal kernel it is safe to sleep in a spot
where we're using STP_ALLOC_SLEEP_FLAGS, but in the realtime kernel it
isn't safe to sleep at that same spot. I guess it also makes sense to
sleep as little as possible when running systemtap on the realtime kernel.
So, I'll withdraw my objection. As long as the switch from
STP_ALLOC_SLEEP_FLAGS to STP_ALLOC_FLAGS only affects the realtime
kernel, I'm OK with it.
--
David Smith
dsmith@redhat.com
Red Hat
http://www.redhat.com
256.217.0141 (direct)
256.837.0057 (fax)
next prev parent reply other threads:[~2015-11-18 17:14 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-17 8:09 stp: rt: replace spin_lock with stp style lock and use yzhu1
2015-11-17 8:09 ` [PATCH 1/1] stp: rt: replace spin_lock with stp style lock and use STP_ALLOC_FLAGS yzhu1
2015-11-17 16:45 ` David Smith
2015-11-18 8:14 ` yzhu1
2015-11-18 17:14 ` David Smith [this message]
2015-11-19 7:53 ` yzhu1
-- strict thread matches above, loose matches on Subject: below --
2015-10-22 7:45 Zhu Yanjun
2015-10-22 7:53 ` yzhu1
2015-10-23 4:04 ` Santosh Shukla
2015-10-26 7:03 ` yzhu1
2015-10-26 8:25 ` yzhu1
2015-10-26 8:43 ` Santosh Shukla
2015-11-17 7:38 ` yzhu1
2015-11-17 7:52 ` Santosh Shukla
2015-10-22 16:34 ` David Smith
2015-10-26 3:19 ` yzhu1
2015-10-26 21:28 ` David Smith
2015-10-27 13:52 ` Frank Ch. Eigler
2015-10-28 2:30 ` yzhu1
2015-10-28 17:09 ` David Smith
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