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author | John Garry <john.garry@huawei.com> | 2020-08-19 23:20:24 +0800 |
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committer | Jens Axboe <axboe@kernel.dk> | 2020-09-03 15:20:47 -0600 |
commit | 32bc15afed04bd73e29d713d8db47818d6aa89af (patch) | |
tree | 5b7c59ec86d31c5b17a400dd8e5bd26445b7e33b /block/blk-mq-sched.c | |
parent | 222a5ae03cdd12e7643f2f64689a39ed547650cb (diff) | |
download | lwn-32bc15afed04bd73e29d713d8db47818d6aa89af.tar.gz lwn-32bc15afed04bd73e29d713d8db47818d6aa89af.zip |
blk-mq: Facilitate a shared sbitmap per tagset
Some SCSI HBAs (such as HPSA, megaraid, mpt3sas, hisi_sas_v3 ..) support
multiple reply queues with single hostwide tags.
In addition, these drivers want to use interrupt assignment in
pci_alloc_irq_vectors(PCI_IRQ_AFFINITY). However, as discussed in [0],
CPU hotplug may cause in-flight IO completion to not be serviced when an
interrupt is shutdown. That problem is solved in commit bf0beec0607d
("blk-mq: drain I/O when all CPUs in a hctx are offline").
However, to take advantage of that blk-mq feature, the HBA HW queuess are
required to be mapped to that of the blk-mq hctx's; to do that, the HBA HW
queues need to be exposed to the upper layer.
In making that transition, the per-SCSI command request tags are no
longer unique per Scsi host - they are just unique per hctx. As such, the
HBA LLDD would have to generate this tag internally, which has a certain
performance overhead.
However another problem is that blk-mq assumes the host may accept
(Scsi_host.can_queue * #hw queue) commands. In commit 6eb045e092ef ("scsi:
core: avoid host-wide host_busy counter for scsi_mq"), the Scsi host busy
counter was removed, which would stop the LLDD being sent more than
.can_queue commands; however, it should still be ensured that the block
layer does not issue more than .can_queue commands to the Scsi host.
To solve this problem, introduce a shared sbitmap per blk_mq_tag_set,
which may be requested at init time.
New flag BLK_MQ_F_TAG_HCTX_SHARED should be set when requesting the
tagset to indicate whether the shared sbitmap should be used.
Even when BLK_MQ_F_TAG_HCTX_SHARED is set, a full set of tags and requests
are still allocated per hctx; the reason for this is that if tags and
requests were only allocated for a single hctx - like hctx0 - it may break
block drivers which expect a request be associated with a specific hctx,
i.e. not always hctx0. This will introduce extra memory usage.
This change is based on work originally from Ming Lei in [1] and from
Bart's suggestion in [2].
[0] https://lore.kernel.org/linux-block/alpine.DEB.2.21.1904051331270.1802@nanos.tec.linutronix.de/
[1] https://lore.kernel.org/linux-block/20190531022801.10003-1-ming.lei@redhat.com/
[2] https://lore.kernel.org/linux-block/ff77beff-5fd9-9f05-12b6-826922bace1f@huawei.com/T/#m3db0a602f095cbcbff27e9c884d6b4ae826144be
Signed-off-by: John Garry <john.garry@huawei.com>
Tested-by: Don Brace<don.brace@microsemi.com> #SCSI resv cmds patches used
Tested-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-mq-sched.c')
-rw-r--r-- | block/blk-mq-sched.c | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index edfc8ea805bc..86d5545342ff 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -560,7 +560,7 @@ static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set, struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx) { - unsigned int flags = set->flags; + unsigned int flags = set->flags & ~BLK_MQ_F_TAG_HCTX_SHARED; if (hctx->sched_tags) { blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx); @@ -574,7 +574,8 @@ static int blk_mq_sched_alloc_tags(struct request_queue *q, unsigned int hctx_idx) { struct blk_mq_tag_set *set = q->tag_set; - unsigned int flags = set->flags; + /* Clear HCTX_SHARED so tags are init'ed */ + unsigned int flags = set->flags & ~BLK_MQ_F_TAG_HCTX_SHARED; int ret; hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests, @@ -596,7 +597,8 @@ static void blk_mq_sched_tags_teardown(struct request_queue *q) int i; queue_for_each_hw_ctx(q, hctx, i) { - unsigned int flags = hctx->flags; + /* Clear HCTX_SHARED so tags are freed */ + unsigned int flags = hctx->flags & ~BLK_MQ_F_TAG_HCTX_SHARED; if (hctx->sched_tags) { blk_mq_free_rq_map(hctx->sched_tags, flags); |