-----Original Message-----
From: Stephen Hemminger <stephen@networkplumber.org>
Sent: Thursday, April 29, 2021 11:06 PM
To: Ruifeng Wang <redacted>
Cc: Honnappa Nagarahalli <redacted>; Konstantin
Ananyev [off-list ref]; dev@dpdk.org;
david.marchand@redhat.com; thomas@monjalon.net; jerinj@marvell.com;
nd [off-list ref]; Gavin Hu [off-list ref]; Steve Capper
[off-list ref]; Ola Liljedahl [off-list ref]
Subject: Re: [dpdk-dev] [PATCH v3 2/2] ring: use wfe to wait for ring tail
update on aarch64

On Thu, 29 Apr 2021 14:35:35 +0000
Ruifeng Wang [off-list ref] wrote:

quoted

quoted

-----Original Message-----
From: Stephen Hemminger <stephen@networkplumber.org>
Sent: Thursday, April 29, 2021 1:17 AM
To: Ruifeng Wang <redacted>
Cc: Honnappa Nagarahalli <redacted>; Konstantin
Ananyev [off-list ref]; dev@dpdk.org;
david.marchand@redhat.com; thomas@monjalon.net;

jerinj@marvell.com;

quoted

quoted

nd [off-list ref]; Gavin Hu [off-list ref]; Steve Capper
[off-list ref]; Ola Liljedahl [off-list ref]
Subject: Re: [dpdk-dev] [PATCH v3 2/2] ring: use wfe to wait for
ring tail update on aarch64

On Sun, 25 Apr 2021 05:56:53 +0000
Ruifeng Wang [off-list ref] wrote:

quoted

Instead of polling for tail to be updated, use wfe instruction.

Signed-off-by: Gavin Hu <redacted>
Signed-off-by: Ruifeng Wang <redacted>
Reviewed-by: Steve Capper <redacted>
Reviewed-by: Ola Liljedahl <redacted>
Reviewed-by: Honnappa Nagarahalli <redacted>
Acked-by: Konstantin Ananyev <redacted>

Looks ok to me, but it does raise an interesting question.
Shouldn't the original code have been using atomic load to look at ht->tail.

This another place where "volatile considered harmful" applies.

Do you mean 'volatile' should be removed from rte_wait_until_equal_xxx

parameters?

quoted

I meant that all access to tail should be via C11 atomic builtin. At that point,
the volatile on the data structure elements does not matter.

Agreed. If synchronization is ensured by using C11 atomic builtin, 'volatile' on elements can be removed.