Re: Big TCG slowdown when using zstd with aarch64

[Juan Quintela]

Daniel P. Berrangé <berrange@redhat.com> wrote:
> On Thu, Jun 01, 2023 at 11:06:42PM +0200, Juan Quintela wrote:
>> 
>> Hi
>> 
>> Before I continue investigating this further, do you have any clue what
>> is going on here.  I am running qemu-system-aarch64 on x86_64.
>
> FYI, the trigger for this behaviour appears to be your recent change
> to stats accounting in:
>
> commit cbec7eb76879d419e7dbf531ee2506ec0722e825 (HEAD)
> Author: Juan Quintela <quintela@redhat.com>
> Date:   Mon May 15 21:57:09 2023 +0200
>
>     migration/multifd: Compute transferred bytes correctly
>     
>     In the past, we had to put the in the main thread all the operations
>     related with sizes due to qemu_file not beeing thread safe.  As now
>     all counters are atomic, we can update the counters just after the
>     do the write.  As an aditional bonus, we are able to use the right
>     value for the compression methods.  Right now we were assuming that
>     there were no compression at all.
>     
>     Signed-off-by: Juan Quintela <quintela@redhat.com>
>     Reviewed-by: Peter Xu <peterx@redhat.com>
>     Message-Id: <20230515195709.63843-17-quintela@redhat.com>
>
>
>
> Before that commit the /aarch64/migration/multifd/tcp/plain/{none,zlib,zstd}
> tests all took 21 seconds eachs.
>
> After that commit the 'none' test takes about 3 seconds, and the zlib/zstd
> test take about 1 second, except when zstd is suddenly very slow.

Slowdown was reported by Fiona.

This series remove the slowdown (it is an intermediate state while I
switch from one counter to another.)

Subject: [PATCH v2 00/20] Next round of migration atomic counters

But to integrate it I have to fix the RDMA fixes that you pointed
yesterday and get the series reviewed (Hint, Hint).

Will try to get the RDMA bits fixed during the day.

Thanks for the report, Juan.