From: Hanna Reitz <hreitz@redhat.com>
To: Emanuele Giuseppe Esposito <eesposit@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>, Fam Zheng <fam@euphon.net>,
qemu-devel@nongnu.org, qemu-block@nongnu.org
Subject: Re: [RFC PATCH 0/6] Removal of Aiocontext lock and usage of subtree drains in aborted transactions
Date: Wed, 15 Dec 2021 13:34:46 +0100 [thread overview]
Message-ID: <3b8029b1-8c24-4495-4433-a4dd19d3b28b@redhat.com> (raw)
In-Reply-To: <5fe9120f-04d7-0cfa-36b0-33c9f1680809@redhat.com>
On 14.12.21 19:10, Emanuele Giuseppe Esposito wrote:
>
>
> On 13/12/2021 15:52, Stefan Hajnoczi wrote:
>> Off-topic: I don't understand the difference between the effects of
>> bdrv_drained_begin() and bdrv_subtree_drained_begin(). Both call
>> aio_disable_external(aio_context) and aio_poll(). bdrv_drained_begin()
>> only polls parents and itself, while bdrv_subtree_drained_begin() also
>> polls children. But why does that distinction matter? I wouldn't know
>> when to use one over the other.
>
> Good point. Now I am wondering the same, so it would be great if
> anyone could clarify it.
As far as I understand, bdrv_drained_begin() is used to drain and stop
requests on a single BDS, whereas bdrv_subtree_drained_begin() drains
the BDS and all of its children. So when you don’t care about lingering
requests in child nodes, then bdrv_drained_begin() suffices.
Hanna
next prev parent reply other threads:[~2021-12-15 12:38 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-13 10:40 [RFC PATCH 0/6] Removal of Aiocontext lock and usage of subtree drains in aborted transactions Emanuele Giuseppe Esposito
2021-12-13 10:40 ` [RFC PATCH 1/6] tests/unit/test-bdrv-drain.c: graph setup functions can't run in coroutines Emanuele Giuseppe Esposito
2021-12-13 10:40 ` [RFC PATCH 2/6] introduce BDRV_POLL_WHILE_UNLOCKED Emanuele Giuseppe Esposito
2021-12-13 10:40 ` [RFC PATCH 3/6] block/io.c: introduce bdrv_subtree_drained_{begin/end}_unlocked Emanuele Giuseppe Esposito
2021-12-13 10:40 ` [RFC PATCH 4/6] block.c: add subtree_drains where needed Emanuele Giuseppe Esposito
2021-12-13 10:40 ` [RFC PATCH 5/6] test-bdrv-drain.c: adapt test to the new subtree drains Emanuele Giuseppe Esposito
2021-12-13 10:40 ` [RFC PATCH 6/6] block/io.c: enable assert_bdrv_graph_writable Emanuele Giuseppe Esposito
2021-12-13 14:52 ` [RFC PATCH 0/6] Removal of Aiocontext lock and usage of subtree drains in aborted transactions Stefan Hajnoczi
2021-12-14 18:10 ` Emanuele Giuseppe Esposito
2021-12-15 12:34 ` Hanna Reitz [this message]
2021-12-16 10:37 ` Kevin Wolf
2021-12-14 16:47 ` Stefan Hajnoczi
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