linux-kernel - Re: [PATCH] mailbox: bcm: Replace tasklet with threaded irq

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-Id: <900BDAE9-8FF1-41C8-B909-D897BCAF3445@broadcom.com>
Date:   Fri, 15 Jan 2021 16:55:21 -0500
From:   Rob Rice <rob.rice@...adcom.com>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     Jassi Brar <jassisinghbrar@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH] mailbox: bcm: Replace tasklet with threaded irq

Davidlohr,

I haven’t worked on this driver for 4 years. So my memory is a little vague. But I have notes that we found using the tasklet was 40% faster than threaded IRQ. We were trying to get performance up. So that seemed important at the time. I’m not prepared to defend that now. :-)

Rob

> On Jan 14, 2021, at 10:53 PM, Davidlohr Bueso <dave@...olabs.net> wrote:
> 
> On Thu, 14 Jan 2021, Jassi Brar wrote:
> 
>> On Thu, Jan 14, 2021 at 6:21 PM Davidlohr Bueso <dave@...olabs.net> wrote:
>>> 
>>> Tasklets have long been deprecated as being too heavy on the system
>>> by running in irq context - and this is not a performance critical
>>> path. If a higher priority process wants to run, it must wait for
>>> the tasklet to finish before doing so.
>>> 
>>> Use a more suitable alternative such as threaded irqs and do the
>>> async work in process context.
>>> 
>>> Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
>>> ---
>> Please cc the author and other contributors to this file, esp when
>> this is vendor specific code.
> 
> So looking at who to Cc I noticed:
> 
> commit 8aef00f090bcbe5237c5a6628e7c000890267efe
> Author: Rob Rice <rob.rice@...adcom.com>
> Date:   Mon Nov 14 13:26:01 2016 -0500
> 
>    mailbox: bcm-pdc: Convert from threaded IRQ to tasklet
> 
>    Previously used threaded IRQs in the PDC driver to defer
>    processing the rx DMA ring after getting an rx done interrupt.
>    Instead, use a tasklet at normal priority for deferred processing.
> 
> ... which is exactly the opposite of what modern Linux should be
> doing. Rob, could this not be done in process context?
> 
> Thanks,
> Davidlohr


-- 
This electronic communication and the information and any files transmitted 
with it, or attached to it, are confidential and are intended solely for 
the use of the individual or entity to whom it is addressed and may contain 
information that is confidential, legally privileged, protected by privacy 
laws, or otherwise restricted from disclosure to anyone else. If you are 
not the intended recipient or the person responsible for delivering the 
e-mail to the intended recipient, you are hereby notified that any use, 
copying, distributing, dissemination, forwarding, printing, or copying of 
this e-mail is strictly prohibited. If you received this e-mail in error, 
please return the e-mail to the sender, delete it from your computer, and 
destroy any printed copy of it.

Download attachment "smime.p7s" of type "application/pkcs7-signature" (4154 bytes)