From: Oleg Nesterov <oleg@redhat.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Chuck Ebbert <cebbert.lkml@gmail.com>,
Sasha Levin <sasha.levin@oracle.com>,
Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Denys Vlasenko <dvlasenk@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [tip:x86/asm] x86: Speed up ___preempt_schedule*() by using THUNK helpers
Date: Sat, 4 Oct 2014 01:51:45 +0200 [thread overview]
Message-ID: <20141003235145.GA4548@redhat.com> (raw)
In-Reply-To: <CALCETrVVeuVc7JC7w3Z_2pCx0y_HAFtm4=FmEp_xNkn3tvnR+A@mail.gmail.com>
On 10/03, Andy Lutomirski wrote:
>
> Is this thing missing a flags or cc clobber:
>
> # define __preempt_schedule() asm ("call ___preempt_schedule")
Well, calling.h says "rflags is clobbered", so probably yes?
> Also, I'm at a loss as to wtf all this code is doing.
>
> There's preempt_schedule, which appears to be a normal C function.
>
> There's ___preempt_schedule, which is written in assembly and calls
> preempt_schedule.
>
> Then there's __preempt_schedule, which is an inline assembler function
> that calls ___preempt_schedule.
>
> Is this all just to make the call sequence for preempt_schedule shorter?
Yes, please look at 1a338ac32ca630f67df25b4a16436cccc314e997
sched, x86: Optimize the preempt_schedule() call
Remove the bloat of the C calling convention out of the
preempt_enable() sites by creating an ASM wrapper which allows us to
do an asm("call ___preempt_schedule") instead.
Oleg.
next prev parent reply other threads:[~2014-10-03 23:56 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-21 18:41 [PATCH v3 0/2] x86: reimplement ___preempt_schedule*() using THUNK helpers Oleg Nesterov
2014-09-21 18:41 ` [PATCH v3 1/2] " Oleg Nesterov
2014-09-24 15:02 ` [tip:x86/asm] x86: Speed up ___preempt_schedule*() by " tip-bot for Oleg Nesterov
2014-10-03 4:50 ` Sasha Levin
2014-10-03 13:39 ` Chuck Ebbert
2014-10-03 21:41 ` Oleg Nesterov
2014-10-03 21:56 ` Andy Lutomirski
2014-10-03 23:48 ` Linus Torvalds
2014-10-03 23:51 ` Oleg Nesterov [this message]
2014-10-03 22:48 ` Chuck Ebbert
2014-10-03 22:53 ` Andy Lutomirski
2014-10-03 23:13 ` H. Peter Anvin
2014-10-03 23:37 ` Oleg Nesterov
2014-10-03 21:16 ` Oleg Nesterov
2014-10-03 23:26 ` Oleg Nesterov
2014-10-04 0:01 ` Linus Torvalds
2014-10-04 0:11 ` Linus Torvalds
2014-10-04 0:33 ` Oleg Nesterov
2014-10-05 20:23 ` [PATCH 0/1] stop the unbound recursion in preempt_schedule_context() Oleg Nesterov
2014-10-05 20:23 ` [PATCH 1/1] " Oleg Nesterov
2014-10-28 11:03 ` [tip:sched/core] sched: " tip-bot for Oleg Nesterov
2014-10-05 23:53 ` [PATCH 0/1] " Oleg Nesterov
2014-10-04 0:19 ` [tip:x86/asm] x86: Speed up ___preempt_schedule*() by using THUNK helpers Oleg Nesterov
2014-09-21 18:42 ` [PATCH v3 2/2] x86, lib/Makefile: remove the unnecessary "+= thunk_64.o" Oleg Nesterov
2014-09-24 15:02 ` [tip:x86/asm] x86/lib/Makefile: Remove " tip-bot for Oleg Nesterov
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