Re: [PATCH 4/4] multifd: reset next_packet_len after sending pages

[Fabiano Rosas <farosas@suse.de>]

Elena Ufimtseva <elena.ufimtseva@oracle.com> writes:

> Sometimes multifd sends just sync packet with no pages
> (normal_num is 0). In this case the old value is being
> preserved and being accounted for while only packet_len
> is being transferred.
> Reset it to 0 after sending and accounting for.
>

Usually you'd finish your commit message here with your Signed off tag
and the comments below would be included after the following ---
sign. That way we can merge this patch without bring the unrelated
discussion along.

> TODO: Fix the same packet ids in the stream.
> with this patch, there is still an issue with the duplicated
> packets ids being sent (with different number of pages/flags).
> See in below multifd_send trace (before this change):
> multifd_send 394.774 pid=55477 id=0x1 packet_num=0x6f0 normal=0x57 flags=0x1 next_packet_size=0x57000
> multifd_send 181.244 pid=55477 id=0x1 packet_num=0x6f0 normal=0x0 flags=0x0 next_packet_size=0x57000
>
> With this commit there are still duplicated packets, but since no pages
> are being sent with sync flag set, next_packet_size is 0:
> multifd_send 27.814 pid=18602 id=0x1 packet_num=0x574 normal=0x7b flags=0x1 next_packet_size=0x7b000
> multifd_send 136054.792 pid=18602 id=0x1 packet_num=0x574 normal=0x0 flags=0x0 next_packet_size=0x0
> If there is a suggestion how to fix this properly, I will be
> glad to use it.

What is going on here? Is it that we're incrementing the
multifd_send_state->packet_num under different locks? Because p->mutex
is per-channel? You could try turning that into an atomic operation
instead.