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

Tue Dec 29 16:38:29 UTC 2015

I noticed that attaching a DVD-Drive from the host leads to HUGE delays. 
I had attached my /dev/sr0 to the guest and even without a DVD in the 
drive this was causing huge lag about once per second.

Best regards
Michael

Am 28.12.2015 um 19:30 schrieb rndbit:
> 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>:
>>
>>             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> wrote:
>>
>>                 Sorry, but how to check DPC Latency?
>>
>>                 2015-10-29 10:08 GMT+08:00 Nick Sukharev
>>                 <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> wrote:
>>
>>                         On 27 October 2015 at 18:38, LordZiru
>>                         <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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