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Fri, 1 Mar 2024 15:17:51 +0000 (GMT) From: Shrikanth Hegde To: mingo@kernel.org, peterz@infradead.org, vincent.guittot@linaro.org Cc: sshegde@linux.ibm.com, yu.c.chen@intel.com, dietmar.eggemann@arm.com, linux-kernel@vger.kernel.org, nysal@linux.ibm.com, aboorvad@linux.ibm.com, srikar@linux.ibm.com, vschneid@redhat.com, pierre.gondois@arm.com, morten.rasmussen@arm.com, qyousef@layalina.io Subject: [PATCH v4 1/2] sched/fair: Add EAS checks before updating overutilized Date: Fri, 1 Mar 2024 20:47:24 +0530 Message-Id: <20240301151725.874604-2-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.39.3 In-Reply-To: <20240301151725.874604-1-sshegde@linux.ibm.com> References: <20240301151725.874604-1-sshegde@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: Sw86H_SlUa7znm7JbZvkSK28nLZKH0Uw X-Proofpoint-ORIG-GUID: yNlbNyxPqk4W5e6Nuo5_hYvltdF-2KPN X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.1011,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2024-03-01_14,2024-03-01_02,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 clxscore=1015 mlxscore=0 lowpriorityscore=0 mlxlogscore=999 spamscore=0 bulkscore=0 adultscore=0 priorityscore=1501 malwarescore=0 phishscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2311290000 definitions=main-2403010127 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1792337595985735972 X-GMAIL-MSGID: 1792337595985735972 Overutilized field of root domain is only used for EAS(energy aware scheduler) to decide whether to do load balance or not. It is not used if EAS not possible. Currently enqueue_task_fair and task_tick_fair accesses, sometime updates this field. In update_sd_lb_stats it is updated often. This causes cache contention due to true sharing and burns a lot of cycles. overload and overutilized are part of the same cacheline. Updating it often invalidates the cacheline. That causes access to overload to slow down due to false sharing. Hence add EAS check before accessing/updating this field. EAS check is optimized at compile time or it is a static branch. Hence it shouldn't cost much. With the patch, both enqueue_task_fair and newidle_balance don't show up as hot routines in perf profile. 6.8-rc4: 7.18% swapper [kernel.vmlinux] [k] enqueue_task_fair 6.78% s [kernel.vmlinux] [k] newidle_balance +patch: 0.14% swapper [kernel.vmlinux] [k] enqueue_task_fair 0.00% swapper [kernel.vmlinux] [k] newidle_balance Minor change: trace_sched_overutilized_tp expect that second argument to be bool. So do a int to bool conversion for that. Fixes: 2802bf3cd936 ("sched/fair: Add over-utilization/tipping point indicator") Reviewed-by: Srikar Dronamraju Signed-off-by: Shrikanth Hegde --- kernel/sched/fair.c | 49 +++++++++++++++++++++++++++------------------ 1 file changed, 30 insertions(+), 19 deletions(-) -- 2.39.3 diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 6a16129f9a5c..a71f8a1506e4 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6670,15 +6670,29 @@ static inline bool cpu_overutilized(int cpu) return !util_fits_cpu(cpu_util_cfs(cpu), rq_util_min, rq_util_max, cpu); } -static inline void update_overutilized_status(struct rq *rq) +static inline void set_rd_overutilized_status(struct root_domain *rd, + unsigned int status) { - if (!READ_ONCE(rq->rd->overutilized) && cpu_overutilized(rq->cpu)) { - WRITE_ONCE(rq->rd->overutilized, SG_OVERUTILIZED); - trace_sched_overutilized_tp(rq->rd, SG_OVERUTILIZED); - } + WRITE_ONCE(rd->overutilized, status); + trace_sched_overutilized_tp(rd, !!status); +} + +static inline void check_update_overutilized_status(struct rq *rq) +{ + /* + * overutilized field is used for load balancing decisions only + * if energy aware scheduler is being used + */ + if (!sched_energy_enabled()) + return; + + if (!READ_ONCE(rq->rd->overutilized) && cpu_overutilized(rq->cpu)) + set_rd_overutilized_status(rq->rd, SG_OVERUTILIZED); } #else -static inline void update_overutilized_status(struct rq *rq) { } +static inline void check_update_overutilized_status(struct rq *rq) { } +static inline void set_rd_overutilized_status(struct root_domain *rd, + unsigned int status) { } #endif /* Runqueue only has SCHED_IDLE tasks enqueued */ @@ -6779,7 +6793,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) * and the following generally works well enough in practice. */ if (!task_new) - update_overutilized_status(rq); + check_update_overutilized_status(rq); enqueue_throttle: assert_list_leaf_cfs_rq(rq); @@ -9902,7 +9916,7 @@ static inline void update_sg_lb_stats(struct lb_env *env, if (nr_running > 1) *sg_status |= SG_OVERLOAD; - if (cpu_overutilized(i)) + if (sched_energy_enabled() && cpu_overutilized(i)) *sg_status |= SG_OVERUTILIZED; #ifdef CONFIG_NUMA_BALANCING @@ -10596,19 +10610,16 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd env->fbq_type = fbq_classify_group(&sds->busiest_stat); if (!env->sd->parent) { - struct root_domain *rd = env->dst_rq->rd; - /* update overload indicator if we are at root domain */ - WRITE_ONCE(rd->overload, sg_status & SG_OVERLOAD); + WRITE_ONCE(env->dst_rq->rd->overload, sg_status & SG_OVERLOAD); /* Update over-utilization (tipping point, U >= 0) indicator */ - WRITE_ONCE(rd->overutilized, sg_status & SG_OVERUTILIZED); - trace_sched_overutilized_tp(rd, sg_status & SG_OVERUTILIZED); - } else if (sg_status & SG_OVERUTILIZED) { - struct root_domain *rd = env->dst_rq->rd; - - WRITE_ONCE(rd->overutilized, SG_OVERUTILIZED); - trace_sched_overutilized_tp(rd, SG_OVERUTILIZED); + if (sched_energy_enabled()) { + set_rd_overutilized_status(env->dst_rq->rd, + sg_status & SG_OVERUTILIZED); + } + } else if (sched_energy_enabled() && (sg_status & SG_OVERUTILIZED)) { + set_rd_overutilized_status(env->dst_rq->rd, SG_OVERUTILIZED); } update_idle_cpu_scan(env, sum_util); @@ -12609,7 +12620,7 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued) task_tick_numa(rq, curr); update_misfit_status(curr, rq); - update_overutilized_status(task_rq(curr)); + check_update_overutilized_status(task_rq(curr)); task_tick_core(rq, curr); }