Re: [PATCH] util/qemu-coroutine: skip global pool lock when pool is empty

[Kevin Wolf <kwolf@redhat.com>]

Am 29.05.2026 um 03:54 hat Bin Guo geschrieben:
> coroutine_pool_refill_local() acquires global_pool_lock on every
> call even when the global pool is empty (global_pool_size == 0).
> Under high I/O concurrency many threads simultaneously attempt to
> refill from an empty global pool, causing unnecessary mutex
> contention.
> 
> Add a fast-path check: read global_pool_size with qatomic_read()
> before acquiring the mutex.  If zero, the global pool is empty and
> we return immediately.  This is a racy read but correctness is
> preserved: the only consequence of a stale read is a missed refill
> opportunity, which will be retried on the next coroutine allocation.
> 
> Signed-off-by: Bin Guo <guobin@linux.alibaba.com>

If you have any benchmark results, putting them in the commit message
would be a good idea. (If you don't have them, you should probably get
them for a patch that is motivated by performance.)

Kevin