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| author | Paul E. McKenney <paulmck@kernel.org> | 2022-06-12 15:00:06 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2022-07-19 11:39:59 -0700 |
| commit | 8f870e6eb8c0c3f9869bf3fcf9db39f86cfcea49 (patch) | |
| tree | eac82d9f1b94aa700ec5514c378569c8062b9cc3 /kernel | |
| parent | a111daf0c53ae91e71fd2bfe7497862d14132e3e (diff) | |
| download | linux-8f870e6eb8c0c3f9869bf3fcf9db39f86cfcea49.tar.bz2 | |
srcu: Block less aggressively for expedited grace periods
Commit 282d8998e997 ("srcu: Prevent expedited GPs and blocking readers
from consuming CPU") fixed a problem where a long-running expedited SRCU
grace period could block kernel live patching. It did so by giving up
on expediting once a given SRCU expedited grace period grew too old.
Unfortunately, this added excessive delays to boots of virtual embedded
systems specifying "-bios QEMU_EFI.fd" to qemu. This commit therefore
makes the transition away from expediting less aggressive, increasing
the per-grace-period phase number of non-sleeping polls of readers from
one to three and increasing the required grace-period age from one jiffy
(actually from zero to one jiffies) to two jiffies (actually from one
to two jiffies).
Fixes: 282d8998e997 ("srcu: Prevent expedited GPs and blocking readers from consuming CPU")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reported-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Reported-by: chenxiang (M)" <chenxiang66@hisilicon.com>
Cc: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Link: https://lore.kernel.org/all/20615615-0013-5adc-584f-2b1d5c03ebfc@linaro.org/
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/rcu/srcutree.c | 20 |
1 files changed, 13 insertions, 7 deletions
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 50ba70f019de..0db7873f4e95 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -513,7 +513,7 @@ static bool srcu_readers_active(struct srcu_struct *ssp) #define SRCU_INTERVAL 1 // Base delay if no expedited GPs pending. #define SRCU_MAX_INTERVAL 10 // Maximum incremental delay from slow readers. -#define SRCU_MAX_NODELAY_PHASE 1 // Maximum per-GP-phase consecutive no-delay instances. +#define SRCU_MAX_NODELAY_PHASE 3 // Maximum per-GP-phase consecutive no-delay instances. #define SRCU_MAX_NODELAY 100 // Maximum consecutive no-delay instances. /* @@ -522,16 +522,22 @@ static bool srcu_readers_active(struct srcu_struct *ssp) */ static unsigned long srcu_get_delay(struct srcu_struct *ssp) { + unsigned long gpstart; + unsigned long j; unsigned long jbase = SRCU_INTERVAL; if (ULONG_CMP_LT(READ_ONCE(ssp->srcu_gp_seq), READ_ONCE(ssp->srcu_gp_seq_needed_exp))) jbase = 0; - if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq))) - jbase += jiffies - READ_ONCE(ssp->srcu_gp_start); - if (!jbase) { - WRITE_ONCE(ssp->srcu_n_exp_nodelay, READ_ONCE(ssp->srcu_n_exp_nodelay) + 1); - if (READ_ONCE(ssp->srcu_n_exp_nodelay) > SRCU_MAX_NODELAY_PHASE) - jbase = 1; + if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq))) { + j = jiffies - 1; + gpstart = READ_ONCE(ssp->srcu_gp_start); + if (time_after(j, gpstart)) + jbase += j - gpstart; + if (!jbase) { + WRITE_ONCE(ssp->srcu_n_exp_nodelay, READ_ONCE(ssp->srcu_n_exp_nodelay) + 1); + if (READ_ONCE(ssp->srcu_n_exp_nodelay) > SRCU_MAX_NODELAY_PHASE) + jbase = 1; + } } return jbase > SRCU_MAX_INTERVAL ? SRCU_MAX_INTERVAL : jbase; } |