Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable
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- To: "H. Peter Anvin" <hpa@xxxxxxxxx>
- Subject: Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable
- From: Borislav Petkov <bp@xxxxxxxxx>
- Date: Wed, 20 Apr 2016 22:45:01 +0200
- Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Michal Hocko <mhocko@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>, Tony Luck <tony.luck@xxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Chris Zankel <chris@xxxxxxxxxx>, Max Filippov <jcmvbkbc@xxxxxxxxx>, x86@xxxxxxxxxx, linux-alpha@xxxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx, linux-s390@xxxxxxxxxxxxxxx, linux-sh@xxxxxxxxxxxxxxx, sparclinux@xxxxxxxxxxxxxxx, linux-xtensa@xxxxxxxxxxxxxxxx, linux-arch@xxxxxxxxxxxxxxx, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
- In-reply-to: <91A11395-ACAA-4043-B770-2DF6CBAED54C@zytor.com>
- List-id: <linux-ia64.vger.kernel.org>
- References: <1460041951-22347-1-git-send-email-mhocko@kernel.org> <1460041951-22347-11-git-send-email-mhocko@kernel.org> <20160413090829.GB29579@gmail.com> <20160413091625.GF14351@dhcp22.suse.cz> <20160413091943.GA17858@gmail.com> <20160413102731.GA29896@gmail.com> <20160413124943.GH14351@dhcp22.suse.cz> <20160420134019.GX3448@twins.programming.kicks-ass.net> <91A11395-ACAA-4043-B770-2DF6CBAED54C@zytor.com>
- User-agent: Mutt/1.5.24 (2015-08-30)
On Wed, Apr 20, 2016 at 11:04:05AM -0700, H. Peter Anvin wrote:
> The reason it breaks is because the same register can't be an
> input-output register and a separate input. However, the input side of
> the input-output is probably undefined, and so gcc may not notice.
So Michal and I talked about this a while ago. Why do we need the '"a"
(sem)' input dependency if '"+a" (ret)' already supplies the same thing?
There's also that "=d" (tmp) thing which we don't really need as an
output, right?
I.e., can we simplify like this?
---
#define ____down_write(sem, slow_path) \
({ \
long tmp = RWSEM_ACTIVE_WRITE_BIAS; \
struct rw_semaphore* ret = sem; \
\
asm volatile("# beginning down_write\n\t" \
LOCK_PREFIX " xadd %[tmp],(%[ret])\n\t" \
/* adds 0xffff0001, returns the old value */ \
" test " __ASM_SEL(%w[tmp],%k[tmp]) "," __ASM_SEL(%w[tmp],%k[tmp]) "\n\t" \
/* was the active mask 0 before? */\
" jz 1f\n" \
" call " slow_path "\n" \
"1:\n" \
"# ending down_write" \
: "+m" (sem->count), [ret] "+a" (ret) \
: [tmp] "d" (tmp) \
: "memory", "cc"); \
ret; \
})
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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