Re: [PATCH 3/4] x86: save user rsp in pt_regs->sp on SYSCALL64 fastpath
From: Ingo Molnar
Date: Tue Mar 10 2015 - 09:28:55 EST
> * Denys Vlasenko <dvlasenk@xxxxxxxxxx> wrote:
> > > So there are now +2 instructions (5 instead of 3) in the
> > > system_call path, but there are -2 instructions in the SYSRETQ
> > > path,
> > Unfortunately, no. [...]
> So I assumed that it was an equivalent transformation, given that
> none of the changelogs spelled out the increase in overhead ...
Also, for future reference, you need to spell out performance costs of
fast path patches very clearly - and that wasn't done here.
That's a big no-no, please don't do it again ...
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