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Date: Fri, 21 Jan 2022 16:46:40 +0300
From: Alexander Fomichev <fomichev.ru@...il.com>
To: Hillf Danton <hdanton@...a.com>
Cc: Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
dmaengine@...r.kernel.org, linux@...ro.com,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC] Scheduler: DMA Engine regression because of sched/fair
changes
On Fri, Jan 21, 2022 at 06:12:17PM +0800, Hillf Danton wrote:
> On Wed, 19 Jan 2022 15:55:13 +0300 Alexander Fomichev wrote:
> >On Tue, Jan 18, 2022 at 10:04:48AM +0800, Hillf Danton wrote:
> >> On Mon, 17 Jan 2022 20:44:19 +0300 Alexander Fomichev wrote:
> >> > On Mon, Jan 17, 2022 at 10:27:01AM +0000, Mel Gorman wrote:
> >> >
> >> > -----< v5.15.8-vanilla >-----
> >> > [17057.866760] dmatest: Added 1 threads using dma0chan0
> >> > [17060.133880] dmatest: Started 1 threads using dma0chan0
> >> > [17060.154343] dmatest: dma0chan0-copy0: summary 1000 tests, 0 failures 49338.85 iops 3157686 KB/s (0)
> >> > [17063.737887] dmatest: Added 1 threads using dma0chan0
> >> > [17065.113838] dmatest: Started 1 threads using dma0chan0
> >> > [17065.137659] dmatest: dma0chan0-copy0: summary 1000 tests, 0 failures 42183.41 iops 2699738 KB/s (0)
> >> > [17100.339989] dmatest: Added 1 threads using dma0chan0
> >> > [17102.190764] dmatest: Started 1 threads using dma0chan0
> >> > [17102.214285] dmatest: dma0chan0-copy0: summary 1000 tests, 0 failures 42844.89 iops 2742073 KB/s (0)
> >> > -----< end >-----
> >> >
> >
> >Just to remind, used dmatest parameters:
> >
> >/sys/module/dmatest/parameters/iterations:1000
> >/sys/module/dmatest/parameters/alignment:-1
> >/sys/module/dmatest/parameters/verbose:N
> >/sys/module/dmatest/parameters/norandom:Y
> >/sys/module/dmatest/parameters/max_channels:0
> >/sys/module/dmatest/parameters/dmatest:0
> >/sys/module/dmatest/parameters/polled:N
> >/sys/module/dmatest/parameters/threads_per_chan:1
> >/sys/module/dmatest/parameters/noverify:Y
> >/sys/module/dmatest/parameters/test_buf_size:1048576
> >/sys/module/dmatest/parameters/transfer_size:65536
> >/sys/module/dmatest/parameters/run:N
> >/sys/module/dmatest/parameters/wait:Y
> >/sys/module/dmatest/parameters/timeout:2000
> >/sys/module/dmatest/parameters/xor_sources:3
> >/sys/module/dmatest/parameters/pq_sources:3
>
>
> See if tuning back down 10 degree can close the gap in iops, in the
> assumption that the prev CPU can be ignored in case of cold cache.
>
> Also want to see the diff in output of "cat /proc/interrupts" before
> and after dmatest, wondering if the dma irq is bond to a CPU core of
> dancing on several ones.
>
> Hillf
>
> +++ x/kernel/sched/fair.c
> @@ -5888,20 +5888,10 @@ static int wake_wide(struct task_struct
> static int
> wake_affine_idle(int this_cpu, int prev_cpu, int sync)
> {
> - /*
> - * If this_cpu is idle, it implies the wakeup is from interrupt
> - * context. Only allow the move if cache is shared. Otherwise an
> - * interrupt intensive workload could force all tasks onto one
> - * node depending on the IO topology or IRQ affinity settings.
> - *
> - * If the prev_cpu is idle and cache affine then avoid a migration.
> - * There is no guarantee that the cache hot data from an interrupt
> - * is more important than cache hot data on the prev_cpu and from
> - * a cpufreq perspective, it's better to have higher utilisation
> - * on one CPU.
> - */
> - if (available_idle_cpu(this_cpu) && cpus_share_cache(this_cpu, prev_cpu))
> - return available_idle_cpu(prev_cpu) ? prev_cpu : this_cpu;
> + /* select this cpu because of cold cache */
> + if (cpus_share_cache(this_cpu, prev_cpu))
> + if (available_idle_cpu(this_cpu))
> + return this_cpu;
>
> if (sync && cpu_rq(this_cpu)->nr_running == 1)
> return this_cpu;
> --
Hi Hillf,
Thanks for the information.
With the recent patch (I called it patch2) the results are following:
-----< 5.15.8-Hillf-Danton-patch2+ noverify=Y >-----
[ 646.568455] dmatest: Added 1 threads using dma0chan0
[ 661.127077] dmatest: Started 1 threads using dma0chan0
[ 661.147156] dmatest: dma0chan0-copy0: summary 1000 tests, 0 failures 50251.25 iops 3216080 KB/s (0)
[ 675.132323] dmatest: Added 1 threads using dma0chan0
[ 676.205829] dmatest: Started 1 threads using dma0chan0
[ 676.225991] dmatest: dma0chan0-copy0: summary 1000 tests, 0 failures 50022.50 iops 3201440 KB/s (0)
[ 703.100813] dmatest: Added 1 threads using dma0chan0
[ 704.933579] dmatest: Started 1 threads using dma0chan0
[ 704.953733] dmatest: dma0chan0-copy0: summary 1000 tests, 0 failures 49950.04 iops 3196803 KB/s (0)
-----< end >-----
Also I have re-run the test with 'noverify=N' option, just for
illustration.
-----< 5.15.8-Hillf-Danton-patch2+ noverify=N >-----
[ 1614.739687] dmatest: Added 1 threads using dma0chan0
[ 1620.346536] dmatest: Started 1 threads using dma0chan0
[ 1623.254880] dmatest: dma0chan0-copy0: summary 1000 tests, 0 failures 23544.92 iops 1506875 KB/s (0)
[ 1634.974200] dmatest: Added 1 threads using dma0chan0
[ 1635.981532] dmatest: Started 1 threads using dma0chan0
[ 1638.892182] dmatest: dma0chan0-copy0: summary 1000 tests, 0 failures 23703.98 iops 1517055 KB/s (0)
[ 1652.878143] dmatest: Added 1 threads using dma0chan0
[ 1655.235130] dmatest: Started 1 threads using dma0chan0
[ 1658.143206] dmatest: dma0chan0-copy0: summary 1000 tests, 0 failures 23526.64 iops 1505705 KB/s (0)
-----< end >-----
/proc/interrupts changes before/after the test:
-----< interrupts.diff >-----
- 184: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6000 0 0 0 0 0 0 0 0 0 0 0 IR-PCI-MSI 103813120-edge 0000:c6:00.2
+ 184: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 9000 0 0 0 0 0 0 0 0 0 0 0 IR-PCI-MSI 103813120-edge 0000:c6:00.2
-----< end >-----
It looks like the MSI handler is called on the same CPU all the time.
--
Regards,
Alexander
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