CPU affinity with ULE scheduler
John Baldwin
jhb at freebsd.org
Mon Nov 17 13:13:57 PST 2008
On Monday 17 November 2008 06:36:40 am Archimedes Gaviola wrote:
> On Mon, Nov 17, 2008 at 7:11 PM, Archimedes Gaviola
> <archimedes.gaviola at gmail.com> wrote:
> > On Fri, Nov 14, 2008 at 12:28 AM, John Baldwin <jhb at freebsd.org> wrote:
> >> On Thursday 13 November 2008 06:55:01 am Archimedes Gaviola wrote:
> >>> On Wed, Nov 12, 2008 at 1:16 AM, John Baldwin <jhb at freebsd.org> wrote:
> >>> > On Monday 10 November 2008 11:32:55 pm Archimedes Gaviola wrote:
> >>> >> On Tue, Nov 11, 2008 at 6:33 AM, John Baldwin <jhb at freebsd.org>
wrote:
> >>> >> > On Monday 10 November 2008 03:33:23 am Archimedes Gaviola wrote:
> >>> >> >> To Whom It May Concerned:
> >>> >> >>
> >>> >> >> Can someone explain or share about ULE scheduler (latest version 2
if
> >>> >> >> I'm not mistaken) dealing with CPU affinity? Is there any existing
> >>> >> >> benchmarks on this with FreeBSD? Because I am currently using 4BSD
> >>> >> >> scheduler and as what I have observed especially on processing
high
> >>> >> >> network load traffic on multiple CPU cores, only one CPU were
being
> >>> >> >> stressed with network interrupt while the rests are mostly in idle
> >>> >> >> state. This is an AMD-64 (4x) dual-core IBM system with GigE
Broadcom
> >>> >> >> network interface cards (bce0 and bce1). Below is the snapshot of
the
> >>> >> >> case.
> >>> >> >
> >>> >> > Interrupts are routed to a single CPU. Since bce0 and bce1 are
both on
> >>> > the
> >>> >> > same interrupt (irq 23), the CPU that interrupt is routed to is
going
> >> to
> >>> > end
> >>> >> > up handling all the interrupts for bce0 and bce1. This not
something
> >> ULE
> >>> > or
> >>> >> > 4BSD have any control over.
> >>> >> >
> >>> >> > --
> >>> >> > John Baldwin
> >>> >> >
> >>> >>
> >>> >> Hi John,
> >>> >>
> >>> >> I'm sorry for the wrong snapshot. Here's the right one with my
concern.
> >>> >>
> >>> >> PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU
COMMAND
> >>> >> 17 root 1 171 52 0K 16K CPU0 0 54:28 95.17%
idle:
> >> cpu0
> >>> >> 15 root 1 171 52 0K 16K CPU2 2 55:55 93.65%
idle:
> >> cpu2
> >>> >> 14 root 1 171 52 0K 16K CPU3 3 58:53 93.55%
idle:
> >> cpu3
> >>> >> 13 root 1 171 52 0K 16K RUN 4 59:14 82.47%
idle:
> >> cpu4
> >>> >> 12 root 1 171 52 0K 16K RUN 5 55:42 82.23%
idle:
> >> cpu5
> >>> >> 16 root 1 171 52 0K 16K CPU1 1 58:13 77.78%
idle:
> >> cpu1
> >>> >> 11 root 1 171 52 0K 16K CPU6 6 54:08 76.17%
idle:
> >> cpu6
> >>> >> 36 root 1 -68 -187 0K 16K WAIT 7 8:50 65.53%
> >>> >> irq23: bce0 bce1
> >>> >> 10 root 1 171 52 0K 16K CPU7 7 48:19 29.79%
idle:
> >> cpu7
> >>> >> 43 root 1 171 52 0K 16K pgzero 2 0:35 1.51%
> >> pagezero
> >>> >> 1372 root 10 20 0 16716K 5764K kserel 6 58:42 0.00% kmd
> >>> >> 4488 root 1 96 0 30676K 4236K select 2 1:51 0.00%
sshd
> >>> >> 18 root 1 -32 -151 0K 16K WAIT 0 1:14 0.00%
swi4:
> >>> > clock s
> >>> >> 20 root 1 -44 -163 0K 16K WAIT 0 0:30 0.00%
swi1:
> >> net
> >>> >> 218 root 1 96 0 3852K 1376K select 0 0:23 0.00%
syslogd
> >>> >> 2171 root 1 96 0 30676K 4224K select 6 0:19 0.00%
sshd
> >>> >>
> >>> >> Actually I was doing a network performance testing on this system
with
> >>> >> FreeBSD-6.2 RELEASE using its default scheduler 4BSD and then I used
a
> >>> >> tool to generate big amount of traffic around 600Mbps-700Mbps
> >>> >> traversing the FreeBSD system in bi-direction, meaning both network
> >>> >> interfaces are receiving traffic. What happened was, the CPU (cpu7)
> >>> >> that handles the (irq 23) on both interfaces consumed big amount of
> >>> >> CPU utilization around 65.53% in which it affects other running
> >>> >> applications and services like sshd and httpd. It's no longer
> >>> >> accessible when traffic is bombarded. With the current situation of
my
> >>> >> FreeBSD system with only one CPU being stressed, I was thinking of
> >>> >> moving to FreeBSD-7.0 RELEASE with the ULE scheduler because I
thought
> >>> >> my concern has something to do with the distributions of load on
> >>> >> multiple CPU cores handled by the scheduler especially at the network
> >>> >> level, processing network load. So, if it is more of interrupt
> >>> >> handling and not on the scheduler, is there a way we can optimize it?
> >>> >> Because if it still routed only to one CPU then for me it's still
> >>> >> inefficient. Who handles interrupt scheduling for bounding CPU in
> >>> >> order to prevent shared IRQ? Is there any improvements with
> >>> >> FreeBSD-7.0 with regards to interrupt handling?
> >>> >
> >>> > It depends. In all likelihood, the interrupts from bce0 and bce1 are
both
> >>> > hardwired to the same interrupt pin and so they will always share the
same
> >>> > ithread when using the legacy INTx interrupts. However, bce(4) parts
do
> >>> > support MSI, and if you try a newer OS snap (6.3 or later) these
devices
> >>> > should use MSI in which case each NIC would be assigned to a separate
CPU.
> >> I
> >>> > would suggest trying 7.0 or a 7.1 release candidate and see if it does
> >>> > better.
> >>> >
> >>> > --
> >>> > John Baldwin
> >>> >
> >>>
> >>> Hi John,
> >>>
> >>> I try 7.0 release and each network interface were already allocated
> >>> separately on different CPU. Here, MSI is already working.
> >>>
> >>> PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU
COMMAND
> >>> 12 root 1 171 ki31 0K 16K CPU6 6 123:55 100.00% idle:
> >> cpu6
> >>> 15 root 1 171 ki31 0K 16K CPU3 3 123:54 100.00% idle:
> >> cpu3
> >>> 14 root 1 171 ki31 0K 16K CPU4 4 123:26 100.00% idle:
> >> cpu4
> >>> 16 root 1 171 ki31 0K 16K CPU2 2 123:15 100.00% idle:
> >> cpu2
> >>> 17 root 1 171 ki31 0K 16K CPU1 1 123:15 100.00% idle:
> >> cpu1
> >>> 37 root 1 -68 - 0K 16K CPU7 7 9:09 100.00%
irq256:
> >> bce0
> >>> 13 root 1 171 ki31 0K 16K CPU5 5 123:49 99.07% idle:
cpu5
> >>> 40 root 1 -68 - 0K 16K WAIT 0 4:40 51.17%
irq257:
> >> bce1
> >>> 18 root 1 171 ki31 0K 16K RUN 0 117:48 49.37% idle:
cpu0
> >>> 11 root 1 171 ki31 0K 16K RUN 7 115:25 0.00% idle:
cpu7
> >>> 19 root 1 -32 - 0K 16K WAIT 0 0:39 0.00% swi4:
> >> clock s
> >>> 14367 root 1 44 0 5176K 3104K select 2 0:01 0.00% dhcpd
> >>> 22 root 1 -16 - 0K 16K - 3 0:01 0.00% yarrow
> >>> 25 root 1 -24 - 0K 16K WAIT 0 0:00 0.00% swi6:
> >> Giant t
> >>> 11658 root 1 44 0 32936K 4540K select 1 0:00 0.00% sshd
> >>> 14224 root 1 44 0 32936K 4540K select 5 0:00 0.00% sshd
> >>> 41 root 1 -60 - 0K 16K WAIT 0 0:00 0.00% irq1:
> >> atkbd0
> >>> 4 root 1 -8 - 0K 16K - 2 0:00 0.00% g_down
> >>>
> >>> The bce0 interface interrupt (irq256) gets stressed out which already
> >>> have 100% of CPU7 while CPU0 is around 51.17%. Any more
> >>> recommendations? Is there anything we can do about optimization with
> >>> MSI?
> >>
> >> Well, on 7.x you can try turning net.isr.direct off (sysctl). However,
it
> >> seems you are hammering your bce0 interface. You might want to try using
> >> polling on bce0 and seeing if it keeps up with the traffic better.
> >>
> >> --
> >> John Baldwin
> >>
> >
> > With net.isr.direct=0, my IBM system lessens CPU utilization per
> > interface (bce0 and bce1) but swi1:net increase its utilization.
> > Can you explained what's happening here? What does net.isr.direct do
> > with the decrease of CPU utilization on its interface? I really wanted
> > to know what happened internally during the packets being processed
> > and received by the interfaces then to the device interrupt up to the
> > software interrupt level because I am confused when enabling/disabling
> > net.isr.direct in sysctl. Is there a tool that can we used to trace
> > this process just to be able to know which part of the kernel internal
> > is doing the bottleneck especially when net.isr.direct=1? By the way
> > with device polling enabled, the system experienced packet errors and
> > the interface throughput is worst, so I avoid using it though.
> >
> > PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMMAND
> >
> > 16 root 1 171 ki31 0K 16K CPU10 a 86:06 89.06% idle:
cpu10
> > 27 root 1 -44 - 0K 16K CPU1 1 34:37 82.67% swi1: net
> > 52 root 1 -68 - 0K 16K WAIT b 51:59 59.77% irq32:
bce1
> > 15 root 1 171 ki31 0K 16K RUN b 69:28 43.16% idle:
cpu11
> > 25 root 1 171 ki31 0K 16K RUN 1 115:35 24.27% idle:
cpu1
> > 51 root 1 -68 - 0K 16K CPU10 a 35:21 13.48% irq31:
bce0
> >
> >
> > Regards,
> > Archimedes
> >
>
> One more thing, I observed that when net.isr.direct=1, bce0 is using
> irq256 and bce1 is using irq257 while net.isr.direct=0, bce0 is now
> using irq31 and bce1 is using irq32. What makes it different?
That is not from net.isr.direcct. irq256/257 is when the bce devices are
using MSI. irq31/32 is when the bce devices are using INTx.
--
John Baldwin
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