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Re: [Qemu-devel] [PATCH v2 0/9] block: Delay poll when ending drained se
Re: [Qemu-devel] [PATCH v2 0/9] block: Delay poll when ending drained sections
Mon, 15 Jul 2019 15:24:09 +0200
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Ping – as this series fixes an abort and a segfault, I would appreciate
(Head over to “Fixes for concurrent block jobs” for even more fixes for
aborts and segfaults.)
On 19.06.19 17:25, Max Reitz wrote:
> This is v2 to “block: Keep track of parent quiescing”.
> Please read this cover letter, because I’m very unsure about the design
> in this series and I’d appreciate some comments.
> As Kevin wrote in his reply to that series, the actual problem is that
> bdrv_drain_invoke() polls on every node whenever ending a drain. This
> may cause graph changes, which is actually forbidden.
> To solve that problem, this series makes the drain code construct a list
> of undrain operations that have been initiated, and then polls all of
> them on the root level once graph changes are acceptable.
> Note that I don’t like this list concept very much, so I’m open to
> Furthermore, all BdrvChildRoles with BDS parents have a broken
> .drained_end() implementation. The documentation clearly states that
> this function is not allowed to poll, but it does. So this series
> changes it to a variant (using the new code) that does not poll.
> There is a catch, which may actually be a problem, I don’t know: The new
> variant of that .drained_end() does not poll at all, never. As
> described above, now every bdrv_drain_invoke() returns an object that
> describes when it will be done and which can thus be polled for. These
> objects are just discarded when using BdrvChildRole.drained_end(). That
> does not feel quite right. It would probably be more correct to let
> BdrvChildRole.drained_end() return these objects so the top level
> bdrv_drained_end() can poll for their completion.
> I decided not to do this, for two reasons:
> (1) Doing so would spill the “list of objects to poll for” design to
> places outside of block/io.c. I don’t like the design very much as
> it is, but I can live with it as long as it’s constrained to the
> core drain code in block/io.c.
> This is made worse by the fact that currently, those objects are of
> type BdrvCoDrainData. But it shouldn’t be a problem to add a new
> type that is externally visible (we only need the AioContext and
> whether bdrv_drain_invoke_entry() is done).
> (2) It seems to work as it is.
> The alternative would be to add the same GSList ** parameter to
> BdrvChildRole.drained_end() that I added in the core drain code in patch
> 2, and then let the .drained_end() implementation fill that with objects
> to poll for. (Which would be accomplished by adding a frontend to
> bdrv_do_drained_end() that lets bdrv_child_cb_drained_poll() pass the
> parameter through.)
> And then we have bdrv_replace_child_noperm(), which actually wants a
> polling BdrvChildRole.drained_end(). So this series adds
> BdrvChildRole.drained_end_unquiesce(), which takes that role (if there
> is any polling to do).
> Note that if I implemented the alternative described above
> (.drained_end() gets said GSList ** parameter), a
> .drained_end_unquiesce() wouldn’t be necessary.
> bdrv_parent_drained_end_single() could just poll the list returned by
> .drained_end() by itself.
> Finally, patches 1, 8, and 9 are unmodified from v1.
> git backport-diff against v1:
> [----] : patches are identical
> [####] : number of functional differences between upstream/downstream patch
> [down] : patch is downstream-only
> The flags [FC] indicate (F)unctional and (C)ontextual differences,
> 001/9:[----] [--] 'block: Introduce BdrvChild.parent_quiesce_counter'
> 002/9:[down] 'block: Add @data_objs to bdrv_drain_invoke()'
> 003/9:[down] 'block: Add bdrv_poll_drain_data_objs()'
> 004/9:[down] 'block: Move polling out of bdrv_drain_invoke()'
> 005/9:[down] 'block: Add @poll to bdrv_parent_drained_end_single()'
> 006/9:[down] 'block: Add bdrv_drained_end_no_poll()'
> 007/9:[down] 'block: Fix BDS children's .drained_end()'
> 008/9:[----] [--] 'iotests: Add @has_quit to vm.shutdown()'
> 009/9:[----] [--] 'iotests: Test commit with a filter on the chain'
> Max Reitz (9):
> block: Introduce BdrvChild.parent_quiesce_counter
> block: Add @data_objs to bdrv_drain_invoke()
> block: Add bdrv_poll_drain_data_objs()
> block: Move polling out of bdrv_drain_invoke()
> block: Add @poll to bdrv_parent_drained_end_single()
> block: Add bdrv_drained_end_no_poll()
> block: Fix BDS children's .drained_end()
> iotests: Add @has_quit to vm.shutdown()
> iotests: Test commit with a filter on the chain
> include/block/block.h | 22 +++++-
> include/block/block_int.h | 23 ++++++
> block.c | 24 +++---
> block/io.c | 155 ++++++++++++++++++++++++++++++-------
> python/qemu/__init__.py | 5 +-
> tests/qemu-iotests/040 | 40 +++++++++-
> tests/qemu-iotests/040.out | 4 +-
> tests/qemu-iotests/255 | 2 +-
> 8 files changed, 231 insertions(+), 44 deletions(-)
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- Re: [Qemu-devel] [PATCH v2 0/9] block: Delay poll when ending drained sections,
Max Reitz <=