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From: Wilco Dijkstra via Libc-alpha <libc-alpha@sourceware.org>
To: "naohirot@fujitsu.com" <naohirot@fujitsu.com>,
	Noah Goldstein <goldstein.w.n@gmail.com>,
	"Lucas A. M. Magalhaes" <lamm@linux.ibm.com>
Cc: GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH] benchtests: Add memset zero fill benchmark tests
Date: Tue, 20 Jul 2021 10:29:52 +0000	[thread overview]
Message-ID: <VE1PR08MB55998AA2ED076F134F522B9D83E29@VE1PR08MB5599.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <TYAPR01MB602543F7E0835D3A4B00DA56DFE29@TYAPR01MB6025.jpnprd01.prod.outlook.com>

Hi Naohiro,

> In case of zero-over-zero, it's very interesting that memset_generic is faster than memset_a64fx.

That's because it uses DC ZVA for the full range rather than only for sizes > 8MB like in memset v2.

> On the other hand, however, in case of zero-over-one, memset_a64fx is faster is faster than memset_generic.
> It may be due to SVE code.

Yes, you get more bandwidth with 512-bit SVE stores than 128-bit Neon stores.

> Comparing the memset_generic performance, that is non SVE code, between zero-over-zero and
> zero-over-one, it seems that a64fx micro-architecture has some zero-over-zero optimization?.

No, that does not prove that the previous value matters, just that storing zeroes is faster.

Cheers,
Wilco

  reply	other threads:[~2021-07-20 10:30 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-13 15:57 [PATCH] benchtests: Add memset zero fill benchmark tests Wilco Dijkstra via Libc-alpha
2021-07-13 18:47 ` Noah Goldstein via Libc-alpha
2021-07-15  8:15   ` naohirot--- via Libc-alpha
2021-07-20  8:51     ` naohirot--- via Libc-alpha
2021-07-20 10:29       ` Wilco Dijkstra via Libc-alpha [this message]
  -- strict thread matches above, loose matches on Subject: below --
2021-07-13  8:22 Naohiro Tamura via Libc-alpha
2021-07-13 13:50 ` Lucas A. M. Magalhaes via Libc-alpha

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