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Re: [Qemu-block] [PATCH 4/4] block: Cater to iscsi with non-power-of-2 d


From: Peter Lieven
Subject: Re: [Qemu-block] [PATCH 4/4] block: Cater to iscsi with non-power-of-2 discard
Date: Tue, 25 Oct 2016 14:12:34 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0

Am 25.10.2016 um 14:09 schrieb Paolo Bonzini:

On 25/10/2016 14:03, Peter Lieven wrote:
Am 01.08.2016 um 11:22 schrieb Paolo Bonzini:
On 28/07/2016 04:39, Eric Blake wrote:
On 07/27/2016 01:25 AM, Fam Zheng wrote:
On Thu, 07/21 13:34, Eric Blake wrote:
+    max_write_zeroes = max_write_zeroes / alignment * alignment;
Not using QEMU_ALIGN_DOWN despite patch 3?
Looks like I missed that on the rebase. Can fix if there is a reason for
a respin.
Since Stefan acked this, I'm applying the patch and fixing it to use
QEMU_ALIGN_DOWN.

Paolo
Hi,

I came across a sort of regression we introduced with the dropping of
head and tail
of an unaligned discard.

The discard alignment that we use to trim the discard request is just a
hint.

I learned on the equallogics that a page (which is this unusal 15MB
large) is
unallocated even if the discard happens in pieces. E.g. in slices of 1MB
requests.

 From my point of view I would like to restore the old behaviour. What do
you think?
The right logic should be the one in Linux: if splitting a request, and
the next starting sector would be misaligned, stop the discard at the
previous aligned sector.  Otherwise leave everything alone.

Just to clarify. I mean the guest would send incremental 1MB discards
we would now drop all of them if the alignment is 15MB. Previously,
we have sent all of the 1MB requests.

Peter




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