Messages in this thread | | | Date | Thu, 17 Oct 2019 14:54:16 +0100 | From | Sudeep Holla <> | Subject | Re: [PATCH V2] arm64: psci: Reduce waiting time of cpu_psci_cpu_kill() |
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On Thu, Oct 17, 2019 at 09:26:15PM +0800, Yunfeng Ye wrote: > > > On 2019/10/16 23:32, Sudeep Holla wrote: > > On Wed, Oct 09, 2019 at 12:45:16PM +0800, Yunfeng Ye wrote: > >> If psci_ops.affinity_info() fails, it will sleep 10ms, which will not > >> take so long in the right case. Use usleep_range() instead of msleep(), > >> reduce the waiting time, and give a chance to busy wait before sleep. > >> > >> Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com> > >> --- > >> V1->V2: > >> - use usleep_range() instead of udelay() after waiting for a while > >> > >> arch/arm64/kernel/psci.c | 17 +++++++++++++---- > >> 1 file changed, 13 insertions(+), 4 deletions(-) > >> > >> diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c > >> index c9f72b2..99b3122 100644 > >> --- a/arch/arm64/kernel/psci.c > >> +++ b/arch/arm64/kernel/psci.c > >> @@ -82,6 +82,7 @@ static void cpu_psci_cpu_die(unsigned int cpu) > >> static int cpu_psci_cpu_kill(unsigned int cpu) > >> { > >> int err, i; > >> + unsigned long timeout; > >> > >> if (!psci_ops.affinity_info) > >> return 0; > >> @@ -91,16 +92,24 @@ static int cpu_psci_cpu_kill(unsigned int cpu) > >> * while it is dying. So, try again a few times. > >> */ > >> > >> - for (i = 0; i < 10; i++) { > >> + i = 0; > >> + timeout = jiffies + msecs_to_jiffies(100); > >> + do { > >> err = psci_ops.affinity_info(cpu_logical_map(cpu), 0); > >> if (err == PSCI_0_2_AFFINITY_LEVEL_OFF) { > >> pr_info("CPU%d killed.\n", cpu); > >> return 0; > >> } > >> > >> - msleep(10); > >> - pr_info("Retrying again to check for CPU kill\n"); > > > > You dropped this message, any particular reason ? > > > When reduce the time interval to 1ms, the print message maybe increase 10 > times. on the other hand, cpu_psci_cpu_kill() will print message on success > or failure, which this retry log is not very necessary. of cource, I think > use pr_info_once() instead of pr_info() is better. >
Yes changing it to pr_info_once is better than dropping it as it gives some indication to the firmware if there's scope for improvement.
> >> - } > >> + /* busy-wait max 1ms */ > >> + if (i++ < 100) { > >> + cond_resched(); > >> + udelay(10); > >> + continue; > > > > Why can't it be simple like loop of 100 * msleep(1) instead of loop of > > 10 * msleep(10). The above initial busy wait for 1 ms looks too much > > optimised for your setup where it takes 50-500us, what if it take just > > over 1 ms ? > > > msleep() is implemented by jiffies. when HZ=100 or HZ=250, msleep(1) is not > accurate. so I think usleep_range() is better. 1 ms looks simple and good, but how > about 100us is better? I refer a function sunxi_mc_smp_cpu_kill(), it use > usleep_range(50, 100). >
Again that's specific to sunxi platforms and may work well. While I agree msleep(1) may not be accurate, I am still inclined to have a max value of 1000(i.e. 1ms) for usleep_range.
-- Regards, Sudeep
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