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Re: [Qemu-devel] [PATCH v2 4/4] libqos/ahci: Swap memread/write with buf
From: |
Paolo Bonzini |
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 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 |
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
- [Qemu-devel] [PATCH v2 0/4] qtest: base64 r/w and faster memset, John Snow, 2015/05/01
- [Qemu-devel] [PATCH v2 2/4] qtest: Add base64 encoded read/write, John Snow, 2015/05/01
- [Qemu-devel] [PATCH v2 1/4] qtest: allow arbitrarily long sends, John Snow, 2015/05/01
- [Qemu-devel] [PATCH v2 3/4] qtest: add memset to qtest protocol, John Snow, 2015/05/01
- [Qemu-devel] [PATCH v2 4/4] libqos/ahci: Swap memread/write with bufread/write, John Snow, 2015/05/01
- Re: [Qemu-devel] [PATCH v2 4/4] libqos/ahci: Swap memread/write with bufread/write,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH v2 4/4] libqos/ahci: Swap memread/write with bufread/write, John Snow, 2015/05/01
- Re: [Qemu-devel] [PATCH v2 4/4] libqos/ahci: Swap memread/write with bufread/write, John Snow, 2015/05/01
- Re: [Qemu-devel] [PATCH v2 4/4] libqos/ahci: Swap memread/write with bufread/write, Paolo Bonzini, 2015/05/05
- Re: [Qemu-devel] [PATCH v2 4/4] libqos/ahci: Swap memread/write with bufread/write, John Snow, 2015/05/05
- Re: [Qemu-devel] [PATCH v2 4/4] libqos/ahci: Swap memread/write with bufread/write, Paolo Bonzini, 2015/05/05
- Re: [Qemu-devel] [PATCH v2 4/4] libqos/ahci: Swap memread/write with bufread/write, John Snow, 2015/05/05