Messages in this thread | | | Subject | Re: [RFC] block: Change the granularity of io ticks from ms to ns | From | Yu Kuai <> | Date | Wed, 7 Dec 2022 21:09:08 +0800 |
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Hi,
在 2022/12/07 11:15, Ming Lei 写道: > On Wed, Dec 07, 2022 at 10:19:08AM +0800, Yu Kuai wrote: >> Hi, >> >> 在 2022/12/07 2:15, Gulam Mohamed 写道: >>> Use ktime to change the granularity of IO accounting in block layer from >>> milli-seconds to nano-seconds to get the proper latency values for the >>> devices whose latency is in micro-seconds. After changing the granularity >>> to nano-seconds the iostat command, which was showing incorrect values for >>> %util, is now showing correct values. >> >> This patch didn't correct the counting of io_ticks, just make the >> error accounting from jiffies(ms) to ns. The problem that util can be >> smaller or larger still exist. > > Agree. > >> >> However, I think this change make sense consider that error margin is >> much smaller, and performance overhead should be minimum. >> >> Hi, Ming, how do you think? > > I remembered that ktime_get() has non-negligible overhead, is there any > test data(iops/cpu utilization) when running fio or t/io_uring on > null_blk with this patch?
Yes, testing with null_blk is necessary, we don't want any performance regression.
BTW, I thought it's fine because it's already used for tracking io latency. > > > Thanks, > Ming > > > . >
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