linux-kernel - Re: Issue: Can padata avoid dealing with CPU-related operations?

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Message-ID: <cwcbhk22vycf6di4d5x56l2e5sxm2o5s45v4w6abqggyluyzko@xhcveoev3vhu>
Date:   Wed, 4 Oct 2023 10:52:57 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Wang Jinchao <wangjinchao@...sion.com>
Cc:     Steffen Klassert <steffen.klassert@...unet.com>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        stone.xulei@...sion.com
Subject: Re: Issue: Can padata avoid dealing with CPU-related operations?

Hi,

On Wed, Sep 27, 2023 at 09:25:54PM +0800, Wang Jinchao wrote:
> Hello, I have a few questions about the padata code I've been studying
> recently:
> 
> - Why does padata use the WQ_UNBOUND attribute of the workqueue?

There's background in this series:
    https://lore.kernel.org/all/20190813005224.30779-1-daniel.m.jordan@oracle.com/

> Because I've noticed a significant maintenance cost related to CPUs.
> Are there any specific benefits?

Aside from what Steffen said about serialization, the pcrypt cpumasks
can be set from sysfs to control where parallel and serial jobs run.

> - In what scenarios is it necessary to specify a CPU for serial
> execution, or is ensuring the order sufficient?

I'm not sure that it's necessary.  The way I read it, at least, it seems
pcrypt uses cb_cpu to load balance serialization across all CPUs allowed
in the serial cpumask.