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Re: [Qemu-devel] [PATCH 3/3] megasas: LSI Megaraid SAS emulation


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH 3/3] megasas: LSI Megaraid SAS emulation
Date: Mon, 04 Jul 2011 08:34:37 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110428 Fedora/3.1.10-1.fc15 Mnenhy/0.8.3 Thunderbird/3.1.10

On 07/04/2011 08:13 AM, Hannes Reinecke wrote:
On 07/03/2011 04:36 PM, Paolo Bonzini wrote:
On 07/02/2011 03:50 PM, Hannes Reinecke wrote:
(And no, I will not getting into another dog-fight with Paul B. here.
Virtio can do without bounce buffers. AHCI can. So I fail to see why
SCSI has to rely on bounce buffers.)

I agree, but I do see why a SCSI device might prefer to rely on
bounce buffers for non-I/O commands. This is why in my last RFC
series for vmw_pvscsi I let the device choose whether to force a
bounce buffer or get an external iovec from the HBA.

Yes, sure, for non-I/O commands it's perfectly okay.
Most of which will be emulated anyway.
It's bounce buffers for I/O which kills performance.

But I seem to have missed your last RFC (I'm not reading qemu-devel on a
regular basis ...).
Care to send me a pointer to it?

Sure, http://lists.gnu.org/archive/html/qemu-devel/2011-06/msg00668.html

Paolo



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