2022-03-11 22:50:45

by Juergen Gross

Subject: [PATCH] xen/blkfront: speed up purge_persistent_grants()

purge_persistent_grants() is scanning the grants list for persistent
grants being no longer in use by the backend. When having found such a
grant, it will be set to "invalid" and pushed to the tail of the list.

Instead of pushing it directly to the end of the list, add it first to
a temporary list, avoiding to scan those entries again in the main
list traversal. After having finished the scan, append the temporary
list to the grant list.

Suggested-by: Jan Beulich <[email protected]>
Signed-off-by: Juergen Gross <[email protected]>
---
drivers/block/xen-blkfront.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index aa996b637d0b..378262ec47ae 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -2533,6 +2533,7 @@ static void purge_persistent_grants(struct blkfront_info *info)

for_each_rinfo(info, rinfo, i) {
struct grant *gnt_list_entry, *tmp;
+ LIST_HEAD(grants);

spin_lock_irqsave(&rinfo->ring_lock, flags);

@@ -2550,9 +2551,11 @@ static void purge_persistent_grants(struct blkfront_info *info)
list_del(&gnt_list_entry->node);
rinfo->persistent_gnts_c--;
gnt_list_entry->gref = GRANT_INVALID_REF;
- list_add_tail(&gnt_list_entry->node, &rinfo->grants);
+ list_add_tail(&gnt_list_entry->node, &grants);
}

+ list_splice_tail(&grants, &rinfo->grants);
+
spin_unlock_irqrestore(&rinfo->ring_lock, flags);
}
}
--
2.34.1

2022-03-11 23:02:45

by Jan Beulich

Subject: Re: [PATCH] xen/blkfront: speed up purge_persistent_grants()

On 11.03.2022 11:35, Juergen Gross wrote:
> purge_persistent_grants() is scanning the grants list for persistent
> grants being no longer in use by the backend. When having found such a
> grant, it will be set to "invalid" and pushed to the tail of the list.
>
> Instead of pushing it directly to the end of the list, add it first to
> a temporary list, avoiding to scan those entries again in the main
> list traversal. After having finished the scan, append the temporary
> list to the grant list.
>
> Suggested-by: Jan Beulich <[email protected]>
> Signed-off-by: Juergen Gross <[email protected]>

Reviewed-by: Jan Beulich <[email protected]>