From: "Michael S. Tsirkin" <mst@redhat.com>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: Gavin Shan <gshan@redhat.com>,
Peter Maydell <peter.maydell@linaro.org>,
qemu-arm@nongnu.org, qemu-devel@nongnu.org, peterx@redhat.com,
alex@shazbot.org, berrange@redhat.com, philmd@oss.qualcomm.com,
philmd@mailo.com, david@kernel.org, clg@redhat.com,
pbonzini@redhat.com, phrdina@redhat.com, jugraham@redhat.com,
liugang24219@sangfor.com.cn, dinghui@sangfor.com.cn,
shan.gavin@gmail.com
Subject: Re: [PATCH v2 1/2] system/memory: Use qemu_ram_{copy, move}() in ram device region accessors
Date: Tue, 16 Jun 2026 00:59:47 -0400 [thread overview]
Message-ID: <20260616005429-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <0038f601-7647-4547-a67a-c6a17fae26ca@linaro.org>
On Mon, Jun 15, 2026 at 09:48:00PM -0700, Richard Henderson wrote:
> On 6/15/26 21:23, Michael S. Tsirkin wrote:
> > B. Also on x86, I do not see why we should not use memcpy for large
> > accesses if we can. Better perf.
>
> We have an example where memcpy writes to the same location 3 times.
> This is not appropriate for any host.
>
>
> r~
Ah, checked libc and sure enough, it does it. E.g. it uses 2 overlapping SSE
stores to do a 17 byte write. Not sure how we get 3 but whatevs.
But just to clarify, I am talking about DMA accesses, that are not
initiated by the VCPU. I am not so sure we care about multiple stores
in this instance? Do we? We do care about speed, for sure.
--
MST
next prev parent reply other threads:[~2026-06-16 5:00 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-15 10:01 [PATCH v2 0/2] system/memory: Make ram device region directly accessible Gavin Shan
2026-06-15 10:01 ` [PATCH v2 1/2] system/memory: Use qemu_ram_{copy, move}() in ram device region accessors Gavin Shan
2026-06-15 10:57 ` Peter Maydell
2026-06-15 14:48 ` Michael S. Tsirkin
2026-06-15 14:56 ` Michael S. Tsirkin
2026-06-15 15:12 ` Peter Maydell
2026-06-15 19:24 ` Gavin Shan
2026-06-15 19:42 ` Michael S. Tsirkin
2026-06-15 21:31 ` Gavin Shan
2026-06-16 4:22 ` Gavin Shan
2026-06-16 4:36 ` Michael S. Tsirkin
2026-06-16 4:23 ` Michael S. Tsirkin
2026-06-16 4:48 ` Richard Henderson
2026-06-16 4:49 ` Michael S. Tsirkin
2026-06-16 4:55 ` Gavin Shan
2026-06-16 5:17 ` Michael S. Tsirkin
2026-06-16 5:21 ` Gavin Shan
2026-06-16 5:32 ` Michael S. Tsirkin
2026-06-16 4:59 ` Michael S. Tsirkin [this message]
2026-06-16 5:07 ` Gavin Shan
2026-06-16 5:25 ` Michael S. Tsirkin
2026-06-15 19:52 ` Michael S. Tsirkin
2026-06-15 15:17 ` Richard Henderson
2026-06-15 16:33 ` Gavin Shan
2026-06-15 17:03 ` Richard Henderson
2026-06-15 18:09 ` Gavin Shan
2026-06-15 18:33 ` Richard Henderson
2026-06-15 19:40 ` Michael S. Tsirkin
2026-06-16 4:18 ` Gavin Shan
2026-06-15 16:35 ` Michael S. Tsirkin
2026-06-15 16:37 ` Michael S. Tsirkin
2026-06-15 17:05 ` Richard Henderson
2026-06-15 10:01 ` [PATCH v2 2/2] system/memory: Make ram device region directly accessible Gavin Shan
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