Messages in this thread | | | Subject | Re: [PATCH RFT] blk-mq: optimize queue tag busy iter for shared_tags | From | John Garry <> | Date | Tue, 21 Dec 2021 15:19:43 +0000 |
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Hi Kashyap,
> This is for current/5.17. This patch is meaningfully only on top of [1]. > > [1] " blk-mq: Use shared tags for shared sbitmap support" Commit - > e155b0c238b20f0a866f4334d292656665836c8a >
But your change seems effectively the same as in https://lore.kernel.org/all/1638794990-137490-4-git-send-email-john.garry@huawei.com/, which is now merged in Jens' 5.17 queue:
https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git/commit/?h=for-5.17/block&id=fea9f92f1748083cb82049ed503be30c3d3a9b69
> While doing additional testing for [1], I noticed some performance issue. > Along with the performance issue, I noticed CPU lockup as well. Lockup > trace - > > _raw_spin_lock_irqsave+0x42/0x50 > blk_mq_find_and_get_req+0x20/0xa0 > bt_iter+0x2d/0x80 > blk_mq_queue_tag_busy_iter+0x1aa/0x2f0 > ? blk_mq_complete_request+0x30/0x30 > ? blk_mq_complete_request+0x30/0x30 > ? __schedule+0x360/0x850 > blk_mq_timeout_work+0x5e/0x120 > process_one_work+0x1a8/0x380 > worker_thread+0x30/0x380 > ? wq_calc_node_cpumask.isra.30+0x100/0x100 > kthread+0x167/0x190 > ? set_kthread_struct+0x40/0x40 > ret_from_fork+0x22/0x30 > > It is a generic performance issue if driver use " shost->host_tagset = 1". > In fact, I found that [1] is useful to fix performance issue and provided > this additional patch. > > I changed my setup to have 64 scsi_devices (earlier I just kept 16 or 24 > drives, so did not noticed this issue). Performance/cpu lockup issue is not > due to [1]. > More number of scsi device, hardware context per host and high queue depth > will increase the chances of lockup and performance drop. > > Do you think, it is good to have changes in 5.16 + stable ? > I don't know if this patch will create any side effect. Can you review and > let me know your feedback. ? >
Can you test my merged change again for this scenario?
I will also note that I mentioned previously that blk_mq_queue_tag_busy_iter() was not optimum for shared sbitmap, i.e. before shared tags, but no one said performance was bad for shared sbitmap.
Thanks, John
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