linux-kernel - Re: [PATCH v3 5/5] x86/entry/64: Bypass enter_from_user

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Message-ID: <20151113152612.GA14397@lerouge>
Date:	Fri, 13 Nov 2015 16:26:13 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Brian Gerst <brgerst@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v3 5/5] x86/entry/64: Bypass enter_from_user_mode on
 non-context-tracking boots

On Thu, Nov 12, 2015 at 12:59:04PM -0800, Andy Lutomirski wrote:
> On CONFIG_CONTEXT_TRACKING kernels that have context tracking
> disabled at runtime (which includes most distro kernels), we still
> have the overhead of a call to enter_from_user_mode in interrupt and
> exception entries.
> 
> If jump labels are available, this uses the jump label
> infrastructure to skip the call.

Looks good. But why are we still calling context tracking code on IRQs at all?

Thanks.
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