On Wed, Sep 04, 2019 at 07:31:48PM +0200, Daniel Lezcano wrote: > Hi, > > On 04/09/2019 19:07, Bart Van Assche wrote: > > On 9/3/19 12:50 AM, Daniel Lezcano wrote: > >> On 03/09/2019 09:28, Ming Lei wrote: > >>> On Tue, Sep 03, 2019 at 08:40:35AM +0200, Daniel Lezcano wrote: > >>>> It is a scheduler problem then ? > >>> > >>> Scheduler can do nothing if the CPU is taken completely by handling > >>> interrupt & softirq, so seems not a scheduler problem, IMO. > >> > >> Why? If there is a irq pressure on one CPU reducing its capacity, the > >> scheduler will balance the tasks on another CPU, no? > > > > Only if CONFIG_IRQ_TIME_ACCOUNTING has been enabled. However, I don't > > know any Linux distro that enables that option. That's probably because > > that option introduces two rdtsc() calls in each interrupt. Given the > > overhead introduced by this option, I don't think this is the solution > > Ming is looking for. > > Was this overhead reported somewhere ? The syscall of gettimeofday() calls ktime_get_real_ts64() which finally calls tk_clock_read() which calls rdtsc too. But gettimeofday() is often used in fast path, and block IO_STAT needs to read it too. > > > See also irqtime_account_irq() in kernel/sched/cputime.c. > > From my POV, this framework could be interesting to detect this situation. Now we are talking about IRQ_TIME_ACCOUNTING instead of IRQ_TIMINGS, and the former one could be used to implement the detection. And the only sharing should be the read of timestamp. Thanks, Ming
