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

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;
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?

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.