linux-kernel - Re: [PATCH 2/9] dma: Convert from tasklet to BH workqueue

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Date: Tue, 2 Apr 2024 18:41:22 +0530
From: Vinod Koul <vkoul@...nel.org>
To: Linus Walleij <linus.walleij@...aro.org>
Cc: Allen Pais <apais@...ux.microsoft.com>, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH 2/9] dma: Convert from tasklet to BH workqueue

On 02-04-24, 14:25, Linus Walleij wrote:
> Hi Allen,
> 
> thanks for your patch!
> 
> On Wed, Mar 27, 2024 at 5:03 PM Allen Pais <apais@...ux.microsoft.com> wrote:
> 
> > The only generic interface to execute asynchronously in the BH context is
> > tasklet; however, it's marked deprecated and has some design flaws. To
> > replace tasklets, BH workqueue support was recently added. A BH workqueue
> > behaves similarly to regular workqueues except that the queued work items
> > are executed in the BH context.
> >
> > This patch converts drivers/dma/* from tasklet to BH workqueue.
> >
> > Based on the work done by Tejun Heo <tj@...nel.org>
> > Branch: git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git for-6.10
> >
> > Signed-off-by: Allen Pais <allen.lkml@...il.com>
> (...)
> > diff --git a/drivers/dma/ste_dma40.c b/drivers/dma/ste_dma40.c
> (...)
> >         if (d40c->pending_tx)
> > -               tasklet_schedule(&d40c->tasklet);
> > +               queue_work(system_bh_wq, &d40c->work);
> 
> Why is "my" driver not allowed to use system_bh_highpri_wq?
> 
> I can't see the reasoning between some drivers using system_bh_wq
> and others being highpri?
> 
> Given the DMA usecase I would expect them all to be high prio.

It didnt use tasklet_hi_schedule(), I guess Allen has done the
conversion of tasklet_schedule -> system_bh_wq and tasklet_hi_schedule
-> system_bh_highpri_wq

Anyway, we are going to use a dma queue so should be better performance

-- 
~Vinod