linux-kernel - Re: [PATCH] firmware: arm_scmi: fix timeout value for send

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Date:   Thu, 11 Jun 2020 09:40:14 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jassi Brar <jassisinghbrar@...il.com>
Cc:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Rob Herring <robh@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "arnd@...db.de" <arnd@...db.de>,
        Sudeep Holla <sudeep.holla@....com>,
        Jassi Brar <jaswinder.singh@...aro.org>
Subject: Re: [PATCH] firmware: arm_scmi: fix timeout value for send_message

On Wed, Jun 10, 2020 at 09:45:55PM -0500, Jassi Brar wrote:
> On Wed, Jun 10, 2020 at 10:56 AM Sudeep Holla <sudeep.holla@....com> wrote:
>
> [I admit you can write bigger posts than me, so I am not going to
> write a passionate response to each of your paragraphs.
> Let's keep it to the point.]
>
> > > > >       if (xfer->hdr.poll_completion) {
> > > > > -             ktime_t stop = ktime_add_ns(ktime_get(), SCMI_MAX_POLL_TO_NS);
> > > > > +             ktime_t stop = ktime_add_ns(ktime_get(), 500 * 1000 * NSEC_PER_USEC);
> > > > >
> > > >
> > > > This is unacceptable delay for schedutil fast_switch. So no for this one.
> > > >
> > > Increasing timeout does not increase latency.
> >
> > Agreed, but worst case you may be stuck here for 500ms which is not
> > acceptable.
> >
> Not acceptable to who, you or the kernel? :)    Now that you said you
> are fixing the scmi's fast_switch implementation.
>

Sorry, I meant to disable it for single channel implementation. I am not
saying we want that on Juno/MHU.

> Even though I don't think 500ms would ruin our lives, but ok, I will
> make it 30ms - same as you did in the 'else' block. And drop the other
> change.

I am fine if cpufreq maintainers allow that in the fast switch path that
happens in the fast path.

--
Regards,
Sudeep