From: Stefan Hajnoczi <stefanha@redhat.com>
To: Fiona Ebner <f.ebner@proxmox.com>
Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, hreitz@redhat.com,
kwolf@redhat.com, fam@euphon.net
Subject: Re: [PATCH 6/6] block/io: keep zero flag for head/tail parts of misaligned zero write when possible
Date: Mon, 2 Feb 2026 17:10:58 -0500 [thread overview]
Message-ID: <20260202221058.GA429972@fedora> (raw)
In-Reply-To: <20260109120837.2772961-7-f.ebner@proxmox.com>
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On Fri, Jan 09, 2026 at 01:08:33PM +0100, Fiona Ebner wrote:
> This fixes io-test 179 with qcow2. Otherwise, there would be more 'data'
> sectors.
>
> Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
> ---
>
> Not sure if we should even attempt this without considering
> detect-zeroes. While it does keep 179 working, it is a change in
> behavior, since it could turn previously data sectors (with zeroes)
> into zero sectors when they are part of the head or tail of a zero
> write.
>
> Would it even be tolerable from a performance perspective?
179 compares qemu-img map output and this makes changes to allocation status
fragile. In a case like this I would either adjust the test case and
regenerate the output, or if the output variance is now unavoidable then
a more sophisticated filter function is needed.
I'd avoid buffer_is_zero() in bdrv_co_do_zero_pwritev() since it eats
CPU cycles.
Stefan
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next prev parent reply other threads:[~2026-02-02 22:14 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-09 12:08 [RFC v2 0/6] block/io: avoid failure caused by misaligned BLKZEROOUT ioctl Fiona Ebner
2026-01-09 12:08 ` [PATCH 1/6] block/io: pass alignment to bdrv_init_padding() Fiona Ebner
2026-01-09 12:08 ` [PATCH 2/6] block/io: add 'bytes' parameter to bdrv_padding_rmw_read() Fiona Ebner
2026-01-09 12:08 ` [PATCH 3/6] block/io: honor pwrite_zeroes_alignment in bdrv_co_do_zero_pwritev() Fiona Ebner
2026-01-09 12:08 ` [PATCH 4/6] block/io: safeguard max transfer calculation in bdrv_aligned_pwritev() Fiona Ebner
2026-01-19 19:34 ` Stefan Hajnoczi
2026-02-05 15:57 ` Kevin Wolf
2026-01-09 12:08 ` [PATCH 5/6] block/io: handle image length not aligned to write zeroes alignment in bdrv_co_do_zero_pwritev() Fiona Ebner
2026-01-09 12:08 ` [PATCH 6/6] block/io: keep zero flag for head/tail parts of misaligned zero write when possible Fiona Ebner
2026-02-02 22:10 ` Stefan Hajnoczi [this message]
2026-01-19 19:38 ` [RFC v2 0/6] block/io: avoid failure caused by misaligned BLKZEROOUT ioctl Stefan Hajnoczi
2026-02-02 22:16 ` Stefan Hajnoczi
2026-02-05 12:13 ` Fiona Ebner
2026-02-05 15:26 ` Stefan Hajnoczi
2026-02-05 16:02 ` Kevin Wolf
2026-05-27 21:06 ` Stefan Hajnoczi
2026-05-28 8:32 ` Fiona Ebner
2026-05-28 13:26 ` Stefan Hajnoczi
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