Re: [PATCH] x86/uaccess: use unrolled string copy for short strings

From	Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Newsgroups	linux.kernel
Subject	Re: [PATCH] x86/uaccess: use unrolled string copy for short strings
Date	2017-06-22 17:00 +0200
Message-ID	<tVbKq-67R-25@gated-at.bofh.it> (permalink)
References	<tULPY-5nY-1@gated-at.bofh.it> <tURLJ-Mh-37@gated-at.bofh.it>
Organization	Intel Corporation

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> > diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h
> > index c5504b9..16a8871 100644
> > --- a/arch/x86/include/asm/uaccess_64.h
> > +++ b/arch/x86/include/asm/uaccess_64.h
> > @@ -28,6 +28,9 @@ copy_user_generic(void *to, const void *from, unsigned len)
> >  {
> >         unsigned ret;
> >
> > +       if (len <= 64)
> > +               return copy_user_generic_unrolled(to, from, len);
> > +

Given this gets inlined surely that should bracketed with an ifdef
against optimizing for space.

Also you give one set of benchmarks but how do they look on different
processors - AMD v Intel, Atom v Core, Ryzen v older AMD etc ?

Alan

Thread

[PATCH] x86/uaccess: use unrolled string copy for short strings Paolo Abeni <pabeni@redhat.com> - 2017-06-21 13:20 +0200
  Re: [PATCH] x86/uaccess: use unrolled string copy for short strings Kees Cook <keescook@chromium.org> - 2017-06-21 19:40 +0200
    Re: [PATCH] x86/uaccess: use unrolled string copy for short strings Alan Cox <gnomes@lxorguk.ukuu.org.uk> - 2017-06-22 17:00 +0200
  Re: [PATCH] x86/uaccess: use unrolled string copy for short strings Ingo Molnar <mingo@kernel.org> - 2017-06-22 10:50 +0200
    Re: [PATCH] x86/uaccess: use unrolled string copy for short strings Paolo Abeni <pabeni@redhat.com> - 2017-06-22 19:10 +0200
  Re: [PATCH] x86/uaccess: use unrolled string copy for short strings Linus Torvalds <torvalds@linux-foundation.org> - 2017-06-22 19:40 +0200
    Re: [PATCH] x86/uaccess: use unrolled string copy for short strings Paolo Abeni <pabeni@redhat.com> - 2017-06-22 20:00 +0200
    [PATCH] x86/uaccess: optimize copy_user_enhanced_fast_string for short string Paolo Abeni <pabeni@redhat.com> - 2017-06-29 16:00 +0200
      Re: [PATCH] x86/uaccess: optimize copy_user_enhanced_fast_string for  short string Linus Torvalds <torvalds@linux-foundation.org> - 2017-06-29 23:50 +0200
      [tip:x86/asm] x86/uaccess: Optimize  copy_user_enhanced_fast_string() for short strings tip-bot for Paolo Abeni <tipbot@zytor.com> - 2017-06-30 15:20 +0200

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