From: Eric Dumazet <edumazet@google.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Alexander Duyck <alexander.duyck@gmail.com>,
Eric Dumazet <eric.dumazet@gmail.com>,
"David S . Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>, netdev <netdev@vger.kernel.org>,
"the arch/x86 maintainers" <x86@kernel.org>
Subject: Re: [PATCH v1] x86/csum: rewrite csum_partial()
Date: Fri, 12 Nov 2021 07:37:48 -0800 [thread overview]
Message-ID: <CANn89iLpjDsSzLCMz6w8TO5zu1N6HoWM3sgzQevv=zpMYaOt8g@mail.gmail.com> (raw)
In-Reply-To: <YY6HXBK7UN4YqBJm@hirez.programming.kicks-ass.net>
On Fri, Nov 12, 2021 at 7:25 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Fri, Nov 12, 2021 at 06:21:38AM -0800, Eric Dumazet wrote:
> > On Fri, Nov 12, 2021 at 1:13 AM Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > > On Thu, Nov 11, 2021 at 02:30:50PM -0800, Eric Dumazet wrote:
> > > > > For values 7 through 1 I wonder if you wouldn't be better served by
> > > > > just doing a single QWORD read and a pair of shifts. Something along
> > > > > the lines of:
> > > > > if (len) {
> > > > > shift = (8 - len) * 8;
> > > > > temp64 = (*(unsigned long)buff << shift) >> shift;
> > > > > result += temp64;
> > > > > result += result < temp64;
> > > > > }
> > > >
> > > > Again, KASAN will not be happy.
> > >
> > > If you do it in asm, kasan will not know, so who cares :-) as long as
> > > the load is aligned, loading beyond @len shouldn't be a problem,
> > > otherwise there's load_unaligned_zeropad().
> >
> > OK, but then in this case we have to align buff on qword boundary,
> > or risk crossing page boundary.
>
> Read the above, use load_unaligned_zeropad(), it's made for exactly that
> case.
>
> Slightly related, see:
>
> https://lkml.kernel.org/r/20211110101326.141775772@infradead.org
Ah right you are, thanks a lot !
next prev parent reply other threads:[~2021-11-12 15:38 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-11 18:10 [PATCH v1] x86/csum: rewrite csum_partial() Eric Dumazet
2021-11-11 21:56 ` Alexander Duyck
2021-11-11 22:30 ` Eric Dumazet
2021-11-12 9:13 ` Peter Zijlstra
2021-11-12 14:21 ` Eric Dumazet
2021-11-12 15:25 ` Peter Zijlstra
2021-11-12 15:37 ` Eric Dumazet [this message]
2021-11-14 14:44 ` David Laight
2021-11-14 15:03 ` Eric Dumazet
2021-11-14 19:09 ` David Laight
2021-11-14 19:23 ` Eric Dumazet
2021-11-14 14:21 ` David Laight
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