Hi,
See the cover letter from v1 for the general idea:
https://lists.nongnu.org/archive/html/qemu-block/2021-06/msg00843.html
The biggest change here in v2 is that instead of having a common CoMutex
protect the block-status cache, we’re using RCU now. So to read from
the cache, or even to invalidate it, no lock is needed, only to update
it with new data.
Disclaimer: I have no experience with RCU in practice so far, neither in
qemu nor anywhere else. So I hope I’ve used it correctly...
Differences to v1 in detail:
- Patch 2:
- Moved BdrvBlockStatusCache.lock up to BDS, it is now the RCU writer
lock
- BDS.block_status_cache is now a pointer, so it can be replaced with
RCU
- Moved all cache access functionality into helper functions
(bdrv_bsc_is_data(), bdrv_bsc_invalidate_range(), bdrv_bsc_fill())
in block.c
- Guard BSC accesses with RCU
(BSC.valid is to be accessed atomically, which allows resetting it
without taking an RCU write lock)
- Check QLIST_EMPTY(&bs->children) not just when reading from the
cache, but when filling it, too (so we don’t need an RCU update when
it won’t make sense)
- Patch 3: Added
- Dropped the block/nbd patch (because it would make NBD query a larger
range; the patch’s intent was to get more information for free, which
this would not be)
git-backport-diff against v1:
Key:
[----] : 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, respectively
001/6:[----] [--] 'block: Drop BDS comment regarding bdrv_append()'
002/6:[0169] [FC] 'block: block-status cache for data regions'
003/6:[down] 'block: Clarify that @bytes is no limit on *pnum'
004/6:[----] [--] 'block/file-posix: Do not force-cap *pnum'
005/6:[----] [--] 'block/gluster: Do not force-cap *pnum'
006/6:[----] [--] 'block/iscsi: Do not force-cap *pnum'
Max Reitz (6):
block: Drop BDS comment regarding bdrv_append()
block: block-status cache for data regions
block: Clarify that @bytes is no limit on *pnum
block/file-posix: Do not force-cap *pnum
block/gluster: Do not force-cap *pnum
block/iscsi: Do not force-cap *pnum
include/block/block_int.h | 54 +++++++++++++++++++++++--
block.c | 84 +++++++++++++++++++++++++++++++++++++++
block/file-posix.c | 7 ++--
block/gluster.c | 7 ++--
block/io.c | 61 ++++++++++++++++++++++++++--
block/iscsi.c | 3 --
6 files changed, 200 insertions(+), 16 deletions(-)
--
2.31.1