linux-kernel - Re: [ANNOUNCE] 4.4-rc6-rt1

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Date:	Thu, 31 Dec 2015 10:24:41 -0600
From:	Clark Williams <williams@...hat.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [ANNOUNCE] 4.4-rc6-rt1

On Wed, 23 Dec 2015 23:57:55 +0100
Sebastian Andrzej Siewior <bigeasy@...utronix.de> 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

Download attachment ".config" of type "application/octet-stream" (155667 bytes)

Download attachment ".config" of type "application/octet-stream" (163184 bytes)