From: Alberto Garcia <berto@igalia.com>
To: Kevin Wolf <kwolf@redhat.com>
Cc: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
qemu-devel@nongnu.org, qemu-block@nongnu.org,
Max Reitz <mreitz@redhat.com>
Subject: Re: [PATCH 0/1] qcow2: Skip copy-on-write when allocating a zero cluster
Date: Mon, 17 Aug 2020 17:58:51 +0200 [thread overview]
Message-ID: <w515z9hz2kk.fsf@maestria.local.igalia.com> (raw)
In-Reply-To: <20200817155307.GS11402@linux.fritz.box>
On Mon 17 Aug 2020 05:53:07 PM CEST, Kevin Wolf wrote:
>> > Or are you saying that ZERO_RANGE + pwrite on a sparse file (=
>> > cluster allocation) is faster for you than just the pwrite alone (=
>> > writing to already allocated cluster)?
>>
>> Yes, 20% faster in my tests (4KB random writes), but in the latter
>> case the cluster is already allocated only at the qcow2 level, not on
>> the filesystem. preallocation=falloc is faster than
>> preallocation=metadata (preallocation=off sits in the middle).
>
> Hm, this feels wrong. Doing more operations should never be faster
> than doing less operations.
>
> Maybe the difference is in allocating 64k at once instead of doing a
> separate allocation for every 4k block?
That's what I imagine, yes. I'll have a look at your patches and tell
you.
Berto
next prev parent reply other threads:[~2020-08-17 16:05 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-14 14:57 [PATCH 0/1] qcow2: Skip copy-on-write when allocating a zero cluster Alberto Garcia
2020-08-14 14:57 ` [PATCH 1/1] " Alberto Garcia
2020-08-14 18:07 ` Vladimir Sementsov-Ogievskiy
2020-08-14 18:06 ` [PATCH 0/1] " Vladimir Sementsov-Ogievskiy
2020-08-17 10:10 ` Kevin Wolf
2020-08-17 15:31 ` Alberto Garcia
2020-08-17 15:53 ` Kevin Wolf
2020-08-17 15:58 ` Alberto Garcia [this message]
2020-08-17 18:18 ` Alberto Garcia
2020-08-18 8:18 ` Kevin Wolf
2020-08-19 14:25 ` Alberto Garcia
2020-08-19 15:07 ` Kevin Wolf
2020-08-19 15:37 ` Alberto Garcia
2020-08-19 15:53 ` Alberto Garcia
2020-08-19 17:53 ` Brian Foster
2020-08-20 20:03 ` Alberto Garcia
2020-08-20 21:58 ` Dave Chinner
2020-08-21 11:05 ` Brian Foster
2020-08-21 11:42 ` Alberto Garcia
2020-08-21 12:12 ` Alberto Garcia
2020-08-21 17:02 ` Brian Foster
2020-08-25 12:24 ` Alberto Garcia
2020-08-25 16:54 ` Brian Foster
2020-08-25 17:18 ` Alberto Garcia
2020-08-25 19:47 ` Brian Foster
2020-08-26 18:34 ` Alberto Garcia
2020-08-27 16:47 ` Brian Foster
2020-08-23 21:59 ` Dave Chinner
2020-08-24 20:14 ` Alberto Garcia
2020-08-21 12:59 ` Brian Foster
2020-08-21 15:51 ` Alberto Garcia
2020-08-23 22:16 ` Dave Chinner
2020-08-21 16:09 ` Alberto Garcia
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