[PATCH 1/3] powerpc/tm: Abort syscalls in active transactions

[Michael Ellerman]

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