Re: [PATCH] coroutine: reserve 5,000 mappings
On Wed, Mar 20, 2024 at 02:12:32PM -0400, Stefan Hajnoczi wrote:
> Daniel P. Berrangé pointed out that the coroutine
> pool size heuristic is very conservative. Instead of halving
> max_map_count, he suggested reserving 5,000 mappings for non-coroutine
> users based on observations of guests he has access to.
>
> Fixes: 86a637e48104 ("coroutine: cap per-thread local pool size")
> Signed-off-by: Stefan Hajnoczi
> ---
> util/qemu-coroutine.c | 15 ++-
> 1 file changed, 10 insertions(+), 5 deletions(-)
Discussed with Kevin and applied to my block tree:
https://gitlab.com/stefanha/qemu/commits/block
Stefan
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Re: [PATCH] coroutine: reserve 5,000 mappings
On Wed, Mar 20, 2024 at 02:12:32PM -0400, Stefan Hajnoczi wrote:
> Daniel P. Berrangé pointed out that the coroutine
> pool size heuristic is very conservative. Instead of halving
> max_map_count, he suggested reserving 5,000 mappings for non-coroutine
> users based on observations of guests he has access to.
>
> Fixes: 86a637e48104 ("coroutine: cap per-thread local pool size")
It wasn't really broken, so "Tweaks" or "Enhances" rather than
"Fixes" if you like :-)
> Signed-off-by: Stefan Hajnoczi
> ---
> util/qemu-coroutine.c | 15 ++-
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c
> index 2790959eaf..eb4eebefdf 100644
> --- a/util/qemu-coroutine.c
> +++ b/util/qemu-coroutine.c
> @@ -377,12 +377,17 @@ static unsigned int get_global_pool_hard_max_size(void)
> NULL) &&
> qemu_strtoi(contents, NULL, 10, &max_map_count) == 0) {
> /*
> - * This is a conservative upper bound that avoids exceeding
> - * max_map_count. Leave half for non-coroutine users like library
> - * dependencies, vhost-user, etc. Each coroutine takes up 2 VMAs so
> - * halve the amount again.
> + * This is an upper bound that avoids exceeding max_map_count. Leave
> a
> + * fixed amount for non-coroutine users like library dependencies,
> + * vhost-user, etc. Each coroutine takes up 2 VMAs so halve the
> + * remaining amount.
> */
> -return max_map_count / 4;
> +if (max_map_count > 5000) {
> +return (max_map_count - 5000) / 2;
> +} else {
> +/* Disable the global pool but threads still have local pools */
> +return 0;
> +}
> }
> #endif
Reviewed-by: Daniel P. Berrangé
With regards,
Daniel
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[PATCH] coroutine: reserve 5,000 mappings
Daniel P. Berrangé pointed out that the coroutine
pool size heuristic is very conservative. Instead of halving
max_map_count, he suggested reserving 5,000 mappings for non-coroutine
users based on observations of guests he has access to.
Fixes: 86a637e48104 ("coroutine: cap per-thread local pool size")
Signed-off-by: Stefan Hajnoczi
---
util/qemu-coroutine.c | 15 ++-
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c
index 2790959eaf..eb4eebefdf 100644
--- a/util/qemu-coroutine.c
+++ b/util/qemu-coroutine.c
@@ -377,12 +377,17 @@ static unsigned int get_global_pool_hard_max_size(void)
NULL) &&
qemu_strtoi(contents, NULL, 10, &max_map_count) == 0) {
/*
- * This is a conservative upper bound that avoids exceeding
- * max_map_count. Leave half for non-coroutine users like library
- * dependencies, vhost-user, etc. Each coroutine takes up 2 VMAs so
- * halve the amount again.
+ * This is an upper bound that avoids exceeding max_map_count. Leave a
+ * fixed amount for non-coroutine users like library dependencies,
+ * vhost-user, etc. Each coroutine takes up 2 VMAs so halve the
+ * remaining amount.
*/
-return max_map_count / 4;
+if (max_map_count > 5000) {
+return (max_map_count - 5000) / 2;
+} else {
+/* Disable the global pool but threads still have local pools */
+return 0;
+}
}
#endif
--
2.44.0
