Re: [ANNOUNCE] 4.4-rc6-rt1

From: Clark Williams
Date: Thu Dec 31 2015 - 11:24:59 EST


On Wed, 23 Dec 2015 23:57:55 +0100
Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote:

> Please don't continue reading before christmas eve (or morning,
> depending on your schedule). If you don't celebrate christmas,
> well go ahead.
>
> Dear RT folks!
>
> I'm pleased to announce the v4.4-rc6-rt1 patch set. I tested it on my
> AMD A10, 64bit. Nothing exploded so far, filesystem is still there.
> I haven't tested it on anything else. Before someone asks: this does not
> mean it does *not* work on ARM I simply did not try it.
>
> If you are brave then download it, install it and have fun. If something
> breaks, please report it. If your machine starts blinking like a
> christmas tree while using the patch then *please* send a photo.
>
> Changes since v4.1.15-rt17:
> - rebase to v4.4-rc6
>
> Known issues (inherited from v4.1-RT):
> - bcache stays disabled
>
> - CPU hotplug is not better than before
>
> - The netlink_release() OOPS, reported by Clark, is still on the
> list, but unsolved due to lack of information
>
> - Christoph Mathys reported a stall in cgroup locking code while using
> Linux containers.
>
> You can get this release via the git tree at:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git v4.4-rc6-rt1
>
> The RT patch against 4.4-rc6 can be found here:
>
> https://cdn.kernel.org/pub/linux/kernel/projects/rt/4.4/patch-4.4-rc6-rt1.patch.xz
>
> The split quilt queue is available at:
>
> https://cdn.kernel.org/pub/linux/kernel/projects/rt/4.4/patches-4.4-rc6-rt1.tar.xz
>
> Sebastian

I pulled this update and tried it on my laptop (i7 quad-core with HT) and an Atom testbox. I'm seeing a change in the cpu utilization of ksoftirqd between 4.1.15-rt17 and 4.4-rc2-rt1, where the per-cpu ksoftirqd threads are running at between 25-40% utilization:

top - 10:15:57 up 13:46, 2 users, load average: 9.44, 9.30, 8.93
Tasks: 188 total, 2 running, 186 sleeping, 0 stopped, 0 zombie
%Cpu(s): 4.7 us, 53.6 sy, 0.0 ni, 37.4 id, 0.1 wa, 0.0 hi, 4.2 si, 0.0 st
KiB Mem : 4046064 total, 480548 free, 179528 used, 3385988 buff/cache
KiB Swap: 5177340 total, 5169908 free, 7432 used. 3785624 avail Mem

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
3 root -2 0 0 0 0 S 37.3 0.0 307:52.44 ksoftirqd/0
32 root -2 0 0 0 0 S 37.3 0.0 308:08.72 ksoftirqd/2
42 root -2 0 0 0 0 R 37.3 0.0 308:32.84 ksoftirqd/3
22 root -2 0 0 0 0 S 26.9 0.0 222:29.82 ksoftirqd/1
1 root 20 0 46628 6980 4976 S 1.3 0.2 0:13.98 systemd
22358 williams 20 0 159980 4552 3780 R 1.0 0.1 0:00.39 top

This is on an otherwise idle box (I had just stopped a kernel compile, hence the load average figures). Normally with my config I see between 2-3% utilization from the ksoftirqd threads.

I've done a small amount of digging and nothing obvious has jumped out at me. Nothing changed in softirq.c, but there were changes in smpboot.c. I've attached the config I used with the 4.4 build.

I'll see what kind of info I can get with ftracing softirq events.

Clark

Attachment: .config
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Attachment: .config
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