diff options
| author | Thomas Gleixner <tglx@linutronix.de> | 2025-11-19 18:27:09 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2025-11-25 19:45:40 +0100 |
| commit | b0c3d51b54f8a4f4c809432d210c0c983d5cd97e (patch) | |
| tree | 7c76e8d9f0631969fa9a2833d950b7394fbb4787 /include | |
| parent | bf070520e398679cd582b3c3e44107bf22c143ba (diff) | |
sched/mmcid: Provide precomputed maximal value
Reading mm::mm_users and mm:::mm_cid::nr_cpus_allowed every time to compute
the maximal CID value is just wasteful as that value is only changing on
fork(), exit() and eventually when the affinity changes.
So it can be easily precomputed at those points and provided in mm::mm_cid
for consumption in the hot path.
But there is an issue with using mm::mm_users for accounting because that
does not necessarily reflect the number of user space tasks as other kernel
code can take temporary references on the MM which skew the picture.
Solve that by adding a users counter to struct mm_mm_cid, which is modified
by fork() and exit() and used for precomputing under mm_mm_cid::lock.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20251119172549.832764634@linutronix.de
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/rseq_types.h | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/include/linux/rseq_types.h b/include/linux/rseq_types.h index d7e8071b626a..0fab369999b6 100644 --- a/include/linux/rseq_types.h +++ b/include/linux/rseq_types.h @@ -117,14 +117,20 @@ struct mm_cid_pcpu { /** * struct mm_mm_cid - Storage for per MM CID data * @pcpu: Per CPU storage for CIDs associated to a CPU + * @max_cids: The exclusive maximum CID value for allocation and convergence * @nr_cpus_allowed: The number of CPUs in the per MM allowed CPUs map. The map * is growth only. + * @users: The number of tasks sharing this MM. Separate from mm::mm_users + * as that is modified by mmget()/mm_put() by other entities which + * do not actually share the MM. * @lock: Spinlock to protect all fields except @pcpu. It also protects * the MM cid cpumask and the MM cidmask bitmap. */ struct mm_mm_cid { struct mm_cid_pcpu __percpu *pcpu; + unsigned int max_cids; unsigned int nr_cpus_allowed; + unsigned int users; raw_spinlock_t lock; }____cacheline_aligned_in_smp; #else /* CONFIG_SCHED_MM_CID */ |