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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2026-05-27 at 10:17 +0200, Vincent Guittot wrote: > On Wed, 27 May 2026 at 09:37, Vincent Guittot > wrote: > >=20 > > On Wed, 27 May 2026 at 03:32, Rik van Riel > > wrote: > > >=20 > > > +++ b/kernel/sched/fair.c > > > @@ -4429,8 +4429,15 @@ static inline void > > > update_tg_load_avg(struct cfs_rq *cfs_rq) > > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* > > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * For migration heav= y workloads, access to tg->load_avg > > > can be > > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * unbound. Limit the= update rate to at most once per ms. > > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */ > > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 now =3D sched_clock_cpu(cpu_of(= rq_of(cfs_rq))); > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * The enclosing PELT upda= te paths always hold rq->lock > > > and have > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * called update_rq_clock(= rq) within microseconds, so rq- > > > >clock_task > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * is fresh.=C2=A0 Use it = instead of sched_clock_cpu() to > > > avoid an rdtsc > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * (plus pipeline serialis= ation) per call -- this > > > function is invoked > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * once per leaf cfs_rq in= __update_blocked_fair(), so on > > > hosts with > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * many cgroups the rdtsc = cost dominates the rate-limit > > > check itself. > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */ > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 now =3D rq_clock_task(rq_of(cfs= _rq)); >=20 > Why not using rq_clock()=C2=A0 ? This removes rdtsc call and still move > forward whatever the irq pressure Good idea, that does seem like a better clock to use! Does that also automatically eliminate the worry about task migration, since update_rq_clock() gets called whenever a task is attached, rqs get attached/detached, and in various other points including the load balancing code? --=20 All Rights Reversed.