linux-kernel - Re: [net-next PATCH] octeontx2-pf: Use only non-isolated cpus in irq affinity

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Date:   Mon, 1 Aug 2022 09:55:51 +0300
From:   Tariq Toukan <ttoukan.linux@...il.com>
To:     Sunil Kovvuri <sunil.kovvuri@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Geetha sowjanya <gakula@...vell.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux Netdev List <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>, edumazet@...gle.com,
        Sunil Kovvuri Goutham <sgoutham@...vell.com>
Subject: Re: [net-next PATCH] octeontx2-pf: Use only non-isolated cpus in irq
 affinity



On 7/27/2022 10:03 AM, Sunil Kovvuri wrote:
> 
> 
> On Wed, Jul 27, 2022 at 11:01 AM Tariq Toukan <ttoukan.linux@...il.com 
> <mailto:ttoukan.linux@...il.com>> wrote:
> 
> 
> 
>     On 7/27/2022 6:08 AM, Jakub Kicinski wrote:
>      > On Mon, 25 Jul 2022 15:14:02 +0530 Geetha sowjanya wrote:
>      >> This patch excludes the isolates cpus from the cpus list
>      >> while setting up TX/RX queue interrupts affinity
>      >>
>      >> Signed-off-by: Geetha sowjanya <gakula@...vell.com
>     <mailto:gakula@...vell.com>>
>      >> Signed-off-by: Sunil Kovvuri Goutham <sgoutham@...vell.com
>     <mailto:sgoutham@...vell.com>>
>      >
>      > Hm, housekeeping_cpumask() looks barely used by drivers,
>      > do you have any references to discussions indicated drivers
>      > are expected to pay attention to it? Really seems like something
>      > that the core should take care of.
>      >
>      > Tariq, thoughts?
> 
>     I agree.
>     IMO this logic best fits inside the new sched API I proposed last week
>     (pending Ack...), transparent to driver.
> 
>     Find here:
>     https://lore.kernel.org/all/20220719162339.23865-2-tariqt@nvidia.com/ <https://lore.kernel.org/all/20220719162339.23865-2-tariqt@nvidia.com/>
> 
> 
> You mean
> 
> +static bool sched_cpus_spread_by_distance(int node, u16 *cpus, int 
> ncpus) +{ +
> 
> .... + cpumask_copy(cpumask, cpu_online_mask);
> 
> Change cpu_online_mask here to a mask which gives non-isolated cores mask ?
> 

Yes that was the intention.
However, on a second thought, I'm not sure this is a good idea.

In some cases, the device driver is isolated-out for other higher prio 
tasks. While in other cases, the device driver processing is the high 
prio task and is isolated in these cpus for best performance.
As the cpus spread usually affects affinity hints and numa-aware 
allocations, your patch might cause a degradation if always applied.