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From: Michael Ellerman <mpe@ellerman.id.au>
To: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: mikey@neuling.org, matt@ozlabs.org, azanella@linux.vnet.ibm.com,
	linuxppc-dev@lists.ozlabs.org,
	Sam Bobroff <sam.bobroff@au1.ibm.com>
Subject: Re: [PATCH 1/3] powerpc/tm: Abort syscalls in active transactions
Date: Tue, 24 Mar 2015 13:04:19 +1100	[thread overview]
Message-ID: <1427162659.28572.3.camel@ellerman.id.au> (raw)
In-Reply-To: <550BE2AB.2050604@linux.vnet.ibm.com>

On Fri, 2015-03-20 at 14:34 +0530, Anshuman Khandual wrote:
> On 03/19/2015 10:13 AM, Sam Bobroff wrote:
> > This patch changes the syscall handler to doom (tabort) active
> > transactions when a syscall is made and return immediately without
> > performing the syscall.
> > 
> > Currently, the system call instruction automatically suspends an
> > active transaction which causes side effects to persist when an active
> > transaction fails.
> > 
> > This does change the kernel's behaviour, but in a way that was
> > documented as unsupported. It doesn't reduce functionality because
> > syscalls will still be performed after tsuspend. It also provides a
> > consistent interface and makes the behaviour of user code
> > substantially the same across powerpc and platforms that do not
> > support suspended transactions (e.g. x86 and s390).
> > 
> > Performance measurements using
> > http://ozlabs.org/~anton/junkcode/null_syscall.c
> > indicate the cost of a system call increases by about 0.5%.
> 
> Performance test results verified which shows an improvement of
> around ~0.52% with the patch compared to without it.
> 
> [With patch]		null_syscall:     757.59 cycles     100.00%
> [Without patch]]	null_syscall:     753.66 cycles     100.00%

No that's a performance *decrease* with the patch applied. ?

cheers

  reply	other threads:[~2015-03-24  2:04 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-19  4:43 [PATCH 0/3] powerpc/tm: Abort syscalls in active transactions Sam Bobroff
2015-03-19  4:43 ` [PATCH 1/3] " Sam Bobroff
2015-03-19  5:01   ` Michael Neuling
2015-03-20  9:04   ` Anshuman Khandual
2015-03-24  2:04     ` Michael Ellerman [this message]
2015-03-24  4:26       ` Anshuman Khandual
2015-03-24 13:02         ` Michael Ellerman
2015-03-19  4:43 ` [PATCH 2/3] selftests/powerpc: Move get_auxv_entry() to harness.c Sam Bobroff
2015-03-19  4:43 ` [PATCH 3/3] selftests/powerpc: Add transactional syscall test Sam Bobroff
2015-03-20  9:25   ` Anshuman Khandual
2015-03-24  1:52     ` Sam Bobroff
2015-03-24  2:02       ` Michael Ellerman
2015-03-30  0:06         ` Sam Bobroff

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