From: Dave Hansen <dave.hansen@intel.com>
To: David Laight <David.Laight@ACULAB.COM>,
'Noah Goldstein' <goldstein.w.n@gmail.com>,
Eric Dumazet <edumazet@google.com>
Cc: "tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
X86 ML <x86@kernel.org>, "hpa@zytor.com" <hpa@zytor.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"alexanderduyck@fb.com" <alexanderduyck@fb.com>,
open list <linux-kernel@vger.kernel.org>,
netdev <netdev@vger.kernel.org>
Subject: Re: [PATCH] x86/lib: Remove the special case for odd-aligned buffers in csum_partial.c
Date: Mon, 13 Dec 2021 07:02:24 -0800 [thread overview]
Message-ID: <52edd5fd-daa0-729b-4646-43450552d2ab@intel.com> (raw)
In-Reply-To: <45d12aa0c95049a392d52ff239d42d83@AcuMS.aculab.com>
On 12/13/21 6:43 AM, David Laight wrote:
> There is no need to special case the very unusual odd-aligned buffers.
> They are no worse than 4n+2 aligned buffers.
>
> Signed-off-by: David Laight <david.laight@aculab.com>
> ---
>
> On an i7-7700 misaligned buffers add 2 or 3 clocks (in 115) to a 512 byte
> checksum.
> That is just measuring the main loop with an lfence prior to rdpmc to
> read PERF_COUNT_HW_CPU_CYCLES.
I'm a bit confused by this changelog.
Are you saying that the patch causes a (small) performance regression?
Are you also saying that the optimization here is not worth it because
it saves 15 lines of code? Or that the misalignment checks themselves
add 2 or 3 cycles, and this is an *optimization*?
next prev parent reply other threads:[~2021-12-13 15:02 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-13 14:43 [PATCH] x86/lib: Remove the special case for odd-aligned buffers in csum_partial.c David Laight
2021-12-13 15:02 ` Dave Hansen [this message]
2021-12-13 15:37 ` David Laight
2021-12-13 15:56 ` Eric Dumazet
2021-12-13 16:16 ` David Laight
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