From: Paolo Abeni <pabeni@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: the arch/x86 maintainers <x86@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Kees Cook <keescook@chromium.org>,
Hannes Frederic Sowa <hannes@stressinduktion.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86/uaccess: use unrolled string copy for short strings
Date: Thu, 22 Jun 2017 19:54:34 +0200 [thread overview]
Message-ID: <1498154074.2503.11.camel@redhat.com> (raw)
In-Reply-To: <CA+55aFzLF6dvHS_N9-M-=6J83HZ3rp+JJ68NSpKc+D_yBA=o_w@mail.gmail.com>
On Thu, 2017-06-22 at 10:30 -0700, Linus Torvalds wrote:
> So if you want to do this optimization, I'd argue that you should just
> do it inside the copy_user_enhanced_fast_string() function itself, the
> same way we already handle the really small case specially in
> copy_user_generic_string().
>
> And do *not* use the unrolled code, which isn't used for small copies
> anyway - rewrite the "copy_user_generic_unrolled" function in that
> same asm file to have the non-unrolled cases (label "17" and forward)
> accessible, so that you don't bother re-testing the size.
Thank you for the feedback.
I'm quite new to the core x86 land; the rep stosb cost popped out while
messing with the networking. I'll try to dig into the asm.
Regards,
Paolo
next prev parent reply other threads:[~2017-06-22 17:54 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-21 11:09 [PATCH] x86/uaccess: use unrolled string copy for short strings Paolo Abeni
2017-06-21 17:38 ` Kees Cook
2017-06-22 14:55 ` Alan Cox
2017-06-22 8:47 ` Ingo Molnar
2017-06-22 17:02 ` Paolo Abeni
2017-06-22 17:30 ` Linus Torvalds
2017-06-22 17:54 ` Paolo Abeni [this message]
2017-06-29 13:55 ` [PATCH] x86/uaccess: optimize copy_user_enhanced_fast_string for short string Paolo Abeni
2017-06-29 21:40 ` Linus Torvalds
2017-06-30 13:10 ` [tip:x86/asm] x86/uaccess: Optimize copy_user_enhanced_fast_string() for short strings tip-bot for Paolo Abeni
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