From: Paolo Bonzini <pbonzini@redhat.com>
To: John Snow <jsnow@redhat.com>, qemu-devel@nongnu.org
Cc: marc.mari.barcelo@gmail.com, afaerber@suse.de, stefanha@redhat.com
Subject: Re: [Qemu-devel] [PATCH v2 4/4] libqos/ahci: Swap memread/write with bufread/write
Date: Fri, 01 May 2015 22:48:08 +0200 [thread overview]
Message-ID: <5543E688.6020703@redhat.com> (raw)
In-Reply-To: <1430510112-30474-5-git-send-email-jsnow@redhat.com>
On 01/05/2015 21:55, John Snow wrote:
> Where it makes sense, use the new faster primitives.
> For generally small reads/writes such as for the PRDT
> and FIS packets, stick with the more wasteful but
> easier to debug memread/memwrite.
>
> For ahci-test;
> With this patch:
> real 0m4.802s
> user 0m3.506s
> sys 0m2.393s
>
> Without this series:
> real 0m14.171s
> user 0m12.072s
> sys 0m12.527s
The overhead of memread is 2, the overhead of base64 is 1.33, also
base64 should have a larger cost of computing each byte. It doesn't add up.
Could it be simply that calling qtest_send (and hence
vsnprintf+qemu_chr_fe_write_all, neither of which are speed demons) once
per byte is hideously inefficient? :)
Paolo
next prev parent reply other threads:[~2015-05-01 20:48 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-01 19:55 [Qemu-devel] [PATCH v2 0/4] qtest: base64 r/w and faster memset John Snow
2015-05-01 19:55 ` [Qemu-devel] [PATCH v2 1/4] qtest: allow arbitrarily long sends John Snow
2015-05-01 19:55 ` [Qemu-devel] [PATCH v2 2/4] qtest: Add base64 encoded read/write John Snow
2015-05-01 19:55 ` [Qemu-devel] [PATCH v2 3/4] qtest: add memset to qtest protocol John Snow
2015-05-01 19:55 ` [Qemu-devel] [PATCH v2 4/4] libqos/ahci: Swap memread/write with bufread/write John Snow
2015-05-01 20:48 ` Paolo Bonzini [this message]
2015-05-01 21:04 ` John Snow
2015-05-02 0:13 ` John Snow
2015-05-05 10:35 ` Paolo Bonzini
2015-05-05 15:48 ` John Snow
2015-05-05 16:19 ` Paolo Bonzini
2015-05-05 16:26 ` John Snow
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