Re: [PATCH 0/3] use C11 memory model GCC builtin atomics

[David Marchand <david.marchand@redhat.com>]

On Mon, Mar 27, 2023 at 4:30 PM Tyler Retzlaff
<roretzla@linux.microsoft.com> wrote:
>
> Replace the use of __sync_<op>_and_fetch and __sync_fetch_and_<op> atomics
> with GCC C11 memory model __atomic builtins.
>
> This series contributes to converging on standard atomics in 23.11 but is
> kept separate as there may be sensitivity to converting from __sync to the
> C11 memory model builtins.

- Looking at the patches, I thought the conversion was rather straightforward.
But this mention about "sensitivity" stopped me from merging.
Did I miss some risk with the changes of this series?


>
> Tyler Retzlaff (3):
>   bus/vmbus: use C11 memory model GCC builtin atomics
>   crypto/ccp: use C11 memory model GCC builtin atomics
>   eal: use C11 memory model GCC builtin atomics
>
>  drivers/bus/vmbus/vmbus_channel.c    |  2 +-
>  drivers/crypto/ccp/ccp_dev.c         |  6 ++++--
>  lib/eal/include/generic/rte_atomic.h | 32 ++++++++++++++++----------------
>  3 files changed, 21 insertions(+), 19 deletions(-)


- I noticed that the vhost library has been providing an internal
wrapper for some __sync atomic with older GCC.
Some details are in the commitlog c16915b87109 ("vhost: improve dirty
pages logging performance").

Could it affect the existing legacy API performance?


-- 
David Marchand