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From: Ingo Molnar <mingo@kernel.org>
To: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Alexei Starovoitov <ast@plumgrid.com>,
	Will Drewry <wad@chromium.org>, Kees Cook <keescook@chromium.org>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/4] x86: save user rsp in pt_regs->sp on SYSCALL64 fastpath
Date: Tue, 10 Mar 2015 14:28:45 +0100	[thread overview]
Message-ID: <20150310132845.GA26490@gmail.com> (raw)
In-Reply-To: <20150310132147.GB26185@gmail.com>


> * Denys Vlasenko <dvlasenk@redhat.com> 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

  parent reply	other threads:[~2015-03-10 13:28 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-09 18:39 [PATCH 0/4 v2] x86: entry_64.S: steps towards simpler iret frame handling Denys Vlasenko
2015-03-09 18:39 ` [PATCH 1/4] x86: save r11 into pt_regs->flags on SYSCALL64 fastpath Denys Vlasenko
2015-03-09 20:02   ` Andy Lutomirski
2015-03-16 12:04   ` [tip:x86/asm] x86/asm/entry/64: Save R11 into pt_regs-> flags " tip-bot for Denys Vlasenko
2015-03-09 18:39 ` [PATCH 3/4] x86: save user rsp in pt_regs->sp " Denys Vlasenko
2015-03-09 20:11   ` Andy Lutomirski
2015-03-09 20:32     ` Denys Vlasenko
2015-03-09 20:43       ` Andy Lutomirski
2015-03-10 12:51   ` Ingo Molnar
2015-03-10 13:10     ` Andy Lutomirski
2015-03-10 13:18     ` Denys Vlasenko
2015-03-10 13:20       ` Andy Lutomirski
2015-03-10 13:26         ` Ingo Molnar
2015-03-10 13:21       ` Ingo Molnar
2015-03-10 13:26         ` Andy Lutomirski
2015-03-10 14:00           ` Denys Vlasenko
2015-03-10 14:02             ` Andy Lutomirski
2015-03-10 14:09               ` Denys Vlasenko
2015-03-10 13:28         ` Ingo Molnar [this message]
2015-03-10 13:50         ` Denys Vlasenko
2015-03-16  9:44           ` Ingo Molnar
2015-03-16 12:05   ` [tip:x86/asm] x86/asm/entry/64: Save user RSP in pt_regs-> sp " tip-bot for Denys Vlasenko
2015-03-10  6:00 ` [PATCH 0/4 v2] x86: entry_64.S: steps towards simpler iret frame handling Ingo Molnar

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