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Re: [libvirt] [PATCH] nodedev_udev: Fix missing events when kernel report lots of udev events within a short time



On Tue, May 09, 2017 at 10:09:07AM +0800, ZhiPeng Lu wrote:
> From: "ning.bo" <ning bo9 zte com cn>
>
> When create Virtual Function for Inter XL710 use below commands:
> for i in `seq 0 1`; do
>         echo 63 > /sys/devices/pci0000:00/0000:00:03.2/0000:07:00.$i/sriov_numvfs
> done
> for i in `seq 0 3`; do
>         echo 31 > /sys/devices/pci0000:80/0000:80:02.2/0000:82:00.$i/sriov_numvfs
> done
>

Hi, I think this is worth a BZ, so we can track and test the issue. Now, I'm
working on a similar issue which is very hard to reproduce and this looks like
it could be reproduced easily with 100% chance, but I don't have any HW to try
it on (it might take a while to get my hands on some). So, would you mind
opening a BZ for this, attaching not only libvirtd's debug logs, but preferably
udev debug logs as well (libudev API is kinda poorly designed in this aspect
and the only way to check for the real error is to enable the debugging and
look into the logs).

> The libvirtd will missing some udev events, the result of libvirt-python API
> listDevices('pci') will not list all pci devices.
> The reason is that the buffer of udev monitor default size cann't save all udev
> events reported by kernel.
> So we need change buffer size so that we can receive as much events as possible
> whitin a short time.
>
> Signed-off-by: ning.bo <ning bo9 zte com cn>
> ---
>  src/node_device/node_device_udev.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/src/node_device/node_device_udev.c b/src/node_device/node_device_udev.c
> index 6e706a1..d813206 100644
> --- a/src/node_device/node_device_udev.c
> +++ b/src/node_device/node_device_udev.c
> @@ -1564,6 +1564,7 @@ static int nodeStateInitialize(bool privileged,
>      }
>
>      udev_monitor_enable_receiving(priv->udev_monitor);
> +    udev_monitor_set_receive_buffer_size(priv->udev_monitor, 128 * 1024 * 1024);
>

The reason why I want to investigate the logs (ideally try it myself) is
rather than blindly increasing the buffer size, maybe we receive just too many
events, out of which some we might filter out and the problem would disappear.
Anyhow, isn't 129 MiB bit of an overkill for a buffer size? I mean, you
didn't provide any commentary on why you chose 128MiB specifically, I can only
guess it somehow relates to the fact, that XL710 is capable of 128 VFs??

Thanks,
Erik

>      /* We register the monitor with the event callback so we are
>       * notified by udev of device changes before we enumerate existing
> --
> 2.8.3
>
>
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