Hitting X limit in launching maximum number of vkcube instances

[Anuj Phogat]

Hi Olivier,

Thanks for experimenting on your end to rule out any X server issues.
I was able to match your results and launch 512 instances of vkcube
after making sure that Xserver (1.21.1.8) has inherited the higher
"max open files" limit. I really appreciate help from you, Adam and Alan.

Anuj

On Wed, Aug 16, 2023 at 12:46 AM Olivier Fourdan <ofourdan at redhat.com> wrote:
>
> Hi Anuj,
>
> On Mon, Aug 14, 2023 at 8:27 PM Anuj Phogat <anuj.phogat at gmail.com> wrote:
>>
>> - I'm still getting the "_XSERVTransSocketUNIXAccept: accept() failed" error
>> after launching ~ 256 instances of vkcube. I was able to find the root
>> cause of error after patching libxtrans based on Adam's suggestion:
>> "_XSERVTransSocketUNIXAccept: accept() failed (Too many open files)"
>> - Based on the hint from the error string, I changed the system wide limit to
>> increase the maximum number of open files allowed from default 1024 to
>> 'ulimit -n' confirmed the new limit. But, this change doesn't change
>> the error past launching ~ 256 instances of vkcube.
>> - I hit the same error but at ~330 instances when I try to run glxgears.
>>
>> Questions:
>> What am I missing when changing the open files limit ?
>
>
> Make sure the X process has inherited that limit, depending on how/where you bumped the limit, the X server process may not have that applied.
>
> You can check using the /proc filesystem on Linux:
>
> $ cat /proc/$(pidof Xorg)/limits
>
>> What else can I try to get past this error ?
>
>
> If you can get 330 instances of glxgears, it means that you are already past the 256 limit, hence the maxclients worked.
>
> It is worth noting that the limit applies to all X11 clients, so if you run a window manager, an xterm, etc, everything counts.
>
> Also if a client opens more than one connection to the X server, that also counts. So you can expect that a limit of 512 might give you a lower actual limit.
>
>>
>> Should I reopen xserver issue [1] or create a new issue to track it ?
>
>
> I doubt that this is an X server issue.
>
> FWIW, I just tried here with Xwayland rootful and was able to run 474 instances of vkcube on a rootful stanlone Xwayland instance:
>
> $ Xwayland -maxclients 512 -decorate :12 7
> $ for i in $(seq 1 512); do DISPLAY=:12 vkcube& done
> $ ps aux | grep vkcube | wc -l
> 474
>
> I have seen some "Maximum number of clients reached" errors while the vkcube instances were spawning en masse, so I suspect maybe the vulkan implementation is opening a connection to the display for some reason temporarily, so having those start all at once may lead to a lower actual limit of clients..
>
> To confirm that theory, I dedid the same test waiting a bit between each instance of vkcube.
>
> And nowI can reach the limit of 512:
>
> $ for i in $(seq 1 512); do DISPLAY=:12 vkcube; sleep .2 & done
> $ ps aux | grep vkcube | wc -l
> 512
>
> So yeah, no bug in the Xserver AFAICS.
>
> This is with:
>
> $ cat /proc/$(pidof Xwayland)/limits
> Limit                     Soft Limit           Hard Limit           Units
> Max cpu time              unlimited            unlimited            seconds
> Max file size             unlimited            unlimited            bytes
> Max data size             unlimited            unlimited            bytes
> Max stack size            8388608              unlimited            bytes
> Max core file size        unlimited            unlimited            bytes
> Max resident set          unlimited            unlimited            bytes
> Max processes             62319                62319                processes
> Max open files            16777216             16777216             files
> Max locked memory         8388608              8388608              bytes
> Max address space         unlimited            unlimited            bytes
> Max file locks            unlimited            unlimited            locks
> Max pending signals       62319                62319                signals
> Max msgqueue size         819200               819200               bytes
> Max nice priority         0                    0
> Max realtime priority     0                    0
> Max realtime timeout      unlimited            unlimited            us
>
>> [1] : https://gitlab.freedesktop.org/xorg/xserver/-/issues/1310
>
>
> Cheers
> Olivier
>
>