[vfio-users] Brutal DPC Latency - how is yours? check it please and report back

rndbit rndbit at sysret.net
Mon Dec 28 18:30:36 UTC 2015


4000μs-16000μs here, its terrible.
Tried whats said on
https://lime-technology.com/forum/index.php?topic=43126.15
Its a bit better with this:
>   <vcpu placement='static'>4</vcpu>
>   <cputune>
>     <vcpupin vcpu='0' cpuset='4'/>
>     <vcpupin vcpu='1' cpuset='5'/>
>     <vcpupin vcpu='2' cpuset='6'/>
>     <vcpupin vcpu='3' cpuset='7'/>
>     <emulatorpin cpuset='0-3'/>
>   </cputune>
I tried /isolcpus/ but it did not yield visible benefits. /ndis.sys/ is
big offender here but i dont really understand why. Removing network
interface from VM makes /usbport.sys/ take over as biggest offender. All
this happens with /performance/ governor of all cpu cores:
> echo performance | tee
> /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor >/dev/null
Cores remain clocked at 4k mhz. I dont know what else i could try. Does
anyone have any ideas..?

On 2015.10.29 08:03, Eddie Yen wrote:
> I tested again with VM reboot, I found that this time is about
> 1000~1500μs.
> Also I found that it easily get high while hard drive is loading, but
> only few times.
>
> Which specs you're using? Maybe it depends on CPU or patches.
>
> 2015-10-29 13:44 GMT+08:00 Blank Field <ihatethisfield at gmail.com
> <mailto:ihatethisfield at gmail.com>>:
>
>     If i understand it right, this software has a fixed latency error
>     of 1 ms(1000us) in windows 8-10 due to different kernel timer
>     implementation. So i guess your latency is very good.
>
>     On Oct 29, 2015 8:40 AM, "Eddie Yen" <missile0407 at gmail.com
>     <mailto:missile0407 at gmail.com>> wrote:
>
>         Thanks for information! And sorry I don'r read carefully at
>         beginning message.
>
>         For my result, I got about 1000μs below and only few times got
>         1000μs above when idling.
>
>         I'm using 4820K and used 4 threads to VM, also  I set these 4
>         threads as 4 cores in VM settings.
>         The OS is Windows 10.
>
>         2015-10-29 13:21 GMT+08:00 Blank Field
>         <ihatethisfield at gmail.com <mailto:ihatethisfield at gmail.com>>:
>
>             I think they're using this:
>             www.thesycon.de/deu/latency_check.shtml
>             <http://www.thesycon.de/deu/latency_check.shtml>
>
>             On Oct 29, 2015 6:11 AM, "Eddie Yen"
>             <missile0407 at gmail.com <mailto:missile0407 at gmail.com>> wrote:
>
>                 Sorry, but how to check DPC Latency?
>
>                 2015-10-29 10:08 GMT+08:00 Nick Sukharev
>                 <nicksukharev at gmail.com <mailto:nicksukharev at gmail.com>>:
>
>                     I just checked on W7 and I get 3000μs-4000μs one
>                     one of the guests when 3 guests are running.
>
>                     On Wed, Oct 28, 2015 at 4:52 AM, Sergey Vlasov
>                     <sergey at vlasov.me <mailto:sergey at vlasov.me>> wrote:
>
>                         On 27 October 2015 at 18:38, LordZiru
>                         <lordziru at gmail.com
>                         <mailto:lordziru at gmail.com>> wrote:
>
>                             I have brutal DPC Latency on qemu, no
>                             matter if using pci-assign or vfio-pci or
>                             without any passthrought,
>
>                             my DPC Latency is like:
>                             10000,500,8000,6000,800,300,12000,9000,700,2000,9000
>                             and on native windows 7 is like:
>                             20,30,20,50,20,30,20,20,30
>
>                          
>                         InWindows 10 guest I constantly have red bars
>                         around 3000μs (microseconds), spiking
>                         sometimes up to 10000μs.
>
>
>                             I don't know how to fix it.
>                             this matter for me because i are using USB
>                             Sound Card for my VMs,
>                             and i get sound drop-outs every 0-4 secounds
>
>
>                         That bugs me a lot too. I also use an external
>                         USB card and my DAW periodically drops out :(
>
>                         I haven't tried CPU pinning yet though. And
>                         perhaps I should try Windows 7.
>
>
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