linux-kernel - Re: [PATCH 3/4] x86: open-code register save/restore in trace

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Message-ID: <20150110204231.GD12218@pd.tnic>
Date:	Sat, 10 Jan 2015 21:42:31 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 3/4] x86: open-code register save/restore in
 trace_hardirqs thunks

On Sat, Jan 10, 2015 at 12:17:13PM -0800, Andy Lutomirski wrote:
> I asked this once, and someone told me that push/pop has lower
> throughput.  I find this surprising.

Implicit dependency on %rsp probably. The MOVs allow you to start more
stuff out-of-order I'd guess...

> Tt could be worth adding a macro along the lines of pushq_cfi_save
> that does the pushq_cfi and the CFI_REL_OFFSET.

Yep, for balance.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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