From: Kevin Wolf <kwolf@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
qemu-devel@nongnu.org,
Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Subject: Re: [Qemu-devel] [PATCH 00/17] Support mismatched host and guest logical block sizes
Date: Wed, 14 Dec 2011 13:05:19 +0100 [thread overview]
Message-ID: <4EE890FF.1050004@redhat.com> (raw)
In-Reply-To: <4EE88CC3.7090903@redhat.com>
Am 14.12.2011 12:47, schrieb Paolo Bonzini:
> On 12/14/2011 12:13 PM, Kevin Wolf wrote:
>> As we discussed before, the really interesting point here is defaults,
>> and whatever you choose to do is wrong in some respect.
>>
>> So it looks like you chose to make the virtual device default to the
>> host block size.
>
> ... wait wait, I default to 512. :)
>
> Here is the rationale. 512-over-4k may be slow, but is safe (but it is
> not slow if you align partitions properly). 4k-over-512 is unsafe. So,
> defaulting to 512 seemed the right thing after all.
Which means bounce buffers by default on 4k hosts. Is this going to
become our next cache=writethrough? At some point 4k disks will be in
wide use, but we'll still be stuck with a slow default of 512.
No matter what we decide here, I think it might really be a good idea to
save the block size in the image and use that as the default if nothing
else is specified on the command line.
Kevin
next prev parent reply other threads:[~2011-12-14 12:02 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-13 12:37 [Qemu-devel] [PATCH 00/17] Support mismatched host and guest logical block sizes Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 01/17] block: do not rely on open_flags for bdrv_is_snapshot Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 02/17] block: store actual flags in bs->open_flags Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 03/17] block: pass protocol flags up to the format Paolo Bonzini
2011-12-15 4:10 ` Zhi Yong Wu
2011-12-13 12:37 ` [Qemu-devel] [PATCH 04/17] block: non-raw protocols never cache Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 05/17] block: remove enable_write_cache Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 06/17] block: move flag bits together Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 07/17] raw: remove the aligned_buf Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 08/17] block: rename buffer_alignment to guest_block_size Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 09/17] block: add host_block_size Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 10/17] raw: probe host_block_size Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 11/17] iscsi: save host block size Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 12/17] block: allow waiting only for overlapping writes Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 13/17] block: allow waiting at arbitrary granularity Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 14/17] block: protect against "torn reads" for guest_block_size > host_block_size Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 15/17] block: align and serialize I/O when guest_block_size < host_block_size Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 16/17] block: default physical block size to host block size Paolo Bonzini
2011-12-13 12:37 ` [Qemu-devel] [PATCH 17/17] qemu-io: add blocksize argument to open Paolo Bonzini
2011-12-14 11:13 ` [Qemu-devel] [PATCH 00/17] Support mismatched host and guest logical block sizes Kevin Wolf
2011-12-14 11:47 ` Paolo Bonzini
2011-12-14 12:05 ` Kevin Wolf [this message]
2011-12-14 12:40 ` Paolo Bonzini
2011-12-21 16:55 ` Christoph Hellwig
2011-12-21 17:00 ` Paolo Bonzini
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