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From: | John Snow |
Subject: | Re: [Qemu-devel] [PATCH v2 4/4] libqos/ahci: Swap memread/write with bufread/write |
Date: | Fri, 01 May 2015 17:04:46 -0400 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 |
On 05/01/2015 04:48 PM, Paolo Bonzini wrote:
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 0m12.527sThe 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.
Right, there's more at play here than just the wire length.
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? :)
I can batch those too in another patch, or should I consider this a NACK?
Paolo
--js
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