linux-kernel - Re: [PATCH] drm/i915: Minimize uaccess exposure in i915_gem_execbuffer2

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Message-ID: <20200228195639.GL23230@ZenIV.linux.org.uk>
Date:   Fri, 28 Feb 2020 19:56:39 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>,
        intel-gfx@...ts.freedesktop.org
Subject: Re: [PATCH] drm/i915: Minimize uaccess exposure in
 i915_gem_execbuffer2_ioctl()

On Fri, Feb 28, 2020 at 07:04:41PM +0100, Peter Zijlstra wrote:
> On Thu, Feb 27, 2020 at 07:03:42PM -0600, Josh Poimboeuf wrote:
> > > And why not mark gen8_canonical_addr() __always_inline?
> > 
> > Right, marking those two functions as __always_inline is the other
> > option.  The problem is, if you keep doing it, eventually you end up
> > with __always_inline-itis spreading all over the place.  And it affects
> > all the other callers, at least in the CONFIG_CC_OPTIMIZE_FOR_SIZE case.
> > At least this fix is localized.
> 
> I'm all for __always_inline in this case, the compiler not inlining sign
> extention is just retarded,

FWIW, in this case it's
        salq    $8, %rax
        sarq    $8, %rax
i.e. 8 bytes.  Sure, that's 3 bytes longer than call, but really, WTF?