Re: [PATCH 3/4] x86: save user rsp in pt_regs->sp on SYSCALL64 fastpath

[Ingo Molnar]

> * 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 ...

Thanks,

	Ingo
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