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Message-ID: <Y5IKuJTjE6Pjrw9I@arm.com>
Date: Thu, 8 Dec 2022 16:03:04 +0000
From: Ionela Voinescu <ionela.voinescu@....com>
To: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Ricardo Neri <ricardo.neri@...el.com>,
"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
Ben Segall <bsegall@...gle.com>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Len Brown <len.brown@...el.com>, Mel Gorman <mgorman@...e.de>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
Steven Rostedt <rostedt@...dmis.org>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Valentin Schneider <vschneid@...hat.com>, x86@...nel.org,
linux-kernel@...r.kernel.org, "Tim C . Chen" <tim.c.chen@...el.com>
Subject: Re: [PATCH v2 5/7] x86/sched: Remove SD_ASYM_PACKING from the "SMT"
domain
Hi Ricardo,
On Tuesday 22 Nov 2022 at 12:35:30 (-0800), Ricardo Neri wrote:
> There is no difference between any of the SMT siblings of a physical core.
> asym_packing load balancing is not needed among siblings.
>
> When balancing load among physical cores, the scheduler now considers the
> state of the siblings when checking the priority of a CPU.
>
> Cc: Ben Segall <bsegall@...gle.com>
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Tim C. Chen <tim.c.chen@...el.com>
> Cc: Valentin Schneider <vschneid@...hat.com>
> Cc: x86@...nel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> ---
> Changes since v1:
> * Introduced this patch.
> ---
> arch/x86/kernel/smpboot.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 3f3ea0287f69..c3de98224cb4 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -545,7 +545,7 @@ static int x86_core_flags(void)
> #ifdef CONFIG_SCHED_SMT
> static int x86_smt_flags(void)
> {
> - return cpu_smt_flags() | x86_sched_itmt_flags();
> + return cpu_smt_flags();
Based on:
kernel/sched/topology.c:
sd = highest_flag_domain(cpu, SD_ASYM_PACKING);
rcu_assign_pointer(per_cpu(sd_asym_packing, cpu), sd);
and described at:
include/linux/sched/sd_flags.h:
/*
* Place busy tasks earlier in the domain
*
* SHARED_CHILD: Usually set on the SMT level. Technically could be set further
* up, but currently assumed to be set from the base domain
* upwards (see update_top_cache_domain()).
* NEEDS_GROUPS: Load balancing flag.
*/
SD_FLAG(SD_ASYM_PACKING, SDF_SHARED_CHILD | SDF_NEEDS_GROUPS)
doesn't your change result in sd_asym_packing being NULL?
The SD_ASYM_PACKING flag requires all children of a domain to have it set
as well. So having SMT not setting the flag, while CLUSTER and MC having
set the flag would result in a broken topology, right?
Thanks,
Ionela.
> }
> #endif
> #ifdef CONFIG_SCHED_CLUSTER
> --
> 2.25.1
>
>
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