linux-kernel - Re: WQ_UNBOUND workqueue warnings from multiple drivers

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Date: Wed, 20 Mar 2024 11:11:16 +0200
From: Sagi Grimberg <sagi@...mberg.me>
To: Kamaljit Singh <Kamaljit.Singh1@....com>,
 "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "kbusch@...nel.org" <kbusch@...nel.org>
Subject: Re: WQ_UNBOUND workqueue warnings from multiple drivers



On 19/03/2024 0:33, Kamaljit Singh wrote:
> Hello,
>
> After switching from Kernel v6.6.2 to v6.6.21 we're now seeing these workqueue
> warnings. I found a discussion thread about the the Intel drm driver here
> https://lore.kernel.org/lkml/ZO-BkaGuVCgdr3wc@slm.duckdns.org/T/
>
> and this related bug report https://gitlab.freedesktop.org/drm/intel/-/issues/9245
> but that that drm fix isn't merged into v6.6.21. It appears that we may need the same
> WQ_UNBOUND change to the nvme host tcp driver among others.
>   
> [Fri Mar 15 22:30:06 2024] workqueue: nvme_tcp_io_work [nvme_tcp] hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND
> [Fri Mar 15 23:44:58 2024] workqueue: drain_vmap_area_work hogged CPU for >10000us 4 times, consider switching to WQ_UNBOUND
> [Sat Mar 16 09:55:27 2024] workqueue: drain_vmap_area_work hogged CPU for >10000us 8 times, consider switching to WQ_UNBOUND
> [Sat Mar 16 17:51:18 2024] workqueue: nvme_tcp_io_work [nvme_tcp] hogged CPU for >10000us 8 times, consider switching to WQ_UNBOUND
> [Sat Mar 16 23:04:14 2024] workqueue: nvme_tcp_io_work [nvme_tcp] hogged CPU for >10000us 16 times, consider switching to WQ_UNBOUND
> [Sun Mar 17 21:35:46 2024] perf: interrupt took too long (2707 > 2500), lowering kernel.perf_event_max_sample_rate to 73750
> [Sun Mar 17 21:49:34 2024] workqueue: drain_vmap_area_work hogged CPU for >10000us 16 times, consider switching to WQ_UNBOUND
> ...
> workqueue: drm_fb_helper_damage_work [drm_kms_helper] hogged CPU for >10000us 32 times, consider switching to WQ_UNBOUND

Hey Kamaljit,

Its interesting that this happens because nvme_tcp_io_work is bound to 1 
jiffie.
Although in theory we do not stop receiving from a socket once we 
started, so
I guess this can happen in some extreme cases. Was the test you were running
read-heavy?

I was thinking that we may want to optionally move the recv path to 
softirq instead to
get some latency improvements, although I don't know if that would 
improve the situation
if we end up spending a lot of time in soft-irq...

>   
>   
> Thanks,
> Kamaljit Singh