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[195.38.112.2]) by smtp.gmail.com with ESMTPSA id fi8-20020a056402550800b0056c509a11acsm1664470edb.33.2024.03.28.23.55.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 Mar 2024 23:55:38 -0700 (PDT) Sender: Ingo Molnar Date: Fri, 29 Mar 2024 07:55:36 +0100 From: Ingo Molnar To: Shrikanth Hegde Cc: peterz@infradead.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, qyousef@layalina.io, linux-kernel@vger.kernel.org, vschneid@redhat.com Subject: Re: [PATCH v3 0/2] sched: Minor changes for rd->overload access Message-ID: References: <20240325054505.201995-1-sshegde@linux.ibm.com> <3c92c18b-6a19-4477-9972-1219c29b3d71@linux.ibm.com> <38c39ea6-21df-44e9-96e7-6f6fd35822a7@linux.ibm.com> <0b5a4432-384c-4470-a7b6-6fcaf8c28236@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0b5a4432-384c-4470-a7b6-6fcaf8c28236@linux.ibm.com> * Shrikanth Hegde wrote: > > > On 3/28/24 4:37 PM, Ingo Molnar wrote: > > > > * Ingo Molnar wrote: > > > >> Plus I've applied a patch to rename ::overload to ::overloaded. It is > >> silly to use an ambiguous noun instead of a clear adjective when naming > >> such a flag ... > > > > Plus SG_OVERLOAD should be SG_OVERLOADED as well - it now looks in line > > with SG_OVERUTILIZED: > > > > /* Scheduling group status flags */ > > #define SG_OVERLOADED 0x1 /* More than one runnable task on a CPU. */ > > #define SG_OVERUTILIZED 0x2 /* One or more CPUs are over-utilized. */ > > > > My followup question is: why are these a bitmask, why not separate > > flags? > > > > AFAICS we only ever set them separately: > > > > thule:~/tip> git grep SG_OVER kernel/sched/ > > kernel/sched/fair.c: set_rd_overutilized_status(rq->rd, SG_OVERUTILIZED); > > kernel/sched/fair.c: *sg_status |= SG_OVERLOADED; > > kernel/sched/fair.c: *sg_status |= SG_OVERUTILIZED; > > kernel/sched/fair.c: *sg_status |= SG_OVERLOADED; > > kernel/sched/fair.c: set_rd_overloaded(env->dst_rq->rd, sg_status & SG_OVERLOADED); > > kernel/sched/fair.c: sg_status & SG_OVERUTILIZED); > > kernel/sched/fair.c: } else if (sg_status & SG_OVERUTILIZED) { > > kernel/sched/fair.c: set_rd_overutilized_status(env->dst_rq->rd, SG_OVERUTILIZED); > > kernel/sched/sched.h:#define SG_OVERLOADED 0x1 /* More than one runnable task on a CPU. */ > > kernel/sched/sched.h:#define SG_OVERUTILIZED 0x2 /* One or more CPUs are over-utilized. */ > > kernel/sched/sched.h: set_rd_overloaded(rq->rd, SG_OVERLOADED); > > > > In fact this results in suboptimal code: > > > > /* update overload indicator if we are at root domain */ > > set_rd_overloaded(env->dst_rq->rd, sg_status & SG_OVERLOADED); > > > > /* Update over-utilization (tipping point, U >= 0) indicator */ > > set_rd_overutilized_status(env->dst_rq->rd, > > sg_status & SG_OVERUTILIZED); > > > > Note how the bits that got mixed together in sg_status now have to be > > masked out individually. > > > > The sg_status bitmask appears to make no sense at all to me. > > > > By turning these into individual bool flags we could also do away with > > all the extra SG_OVERLOADED/SG_OVERUTILIZED abstraction. > > > > Ie. something like the patch below? Untested. > > Looks good. I see it is merged to sched/core. > Did a boot with that patch and hackbench is showing same results 320 CPU system. Thanks, I've added: Acked-by: Shrikanth Hegde Tested-by: Shrikanth Hegde And applied the additional docbook fix below on top as well. Thaks, Ingo =================> kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index ebc8d5f855de..1dd37168da50 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9933,7 +9933,8 @@ sched_reduced_capacity(struct rq *rq, struct sched_domain *sd) * @sds: Load-balancing data with statistics of the local group. * @group: sched_group whose statistics are to be updated. * @sgs: variable to hold the statistics for this group. - * @sg_status: Holds flag indicating the status of the sched_group + * @sg_overloaded: sched_group is overloaded + * @sg_overutilized: sched_group is overutilized */ static inline void update_sg_lb_stats(struct lb_env *env, struct sd_lb_stats *sds,