From: Konstantin Ananyev <konstantin.ananyev@huawei.com>
To: Jack Min <jackmin@nvidia.com>,
Stephen Hemminger <stephen@networkplumber.org>,
Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>, Matan Azrad <matan@nvidia.com>,
"viacheslavo@nvidia.com" <viacheslavo@nvidia.com>,
Tyler Retzlaff <roretzla@linux.microsoft.com>,
Wathsala Wathawana Vithanage <wathsala.vithanage@arm.com>,
nd <nd@arm.com>
Subject: RE: MLX5 PMD access ring library private data
Date: Fri, 18 Aug 2023 09:05:26 +0000 [thread overview]
Message-ID: <cc47fed3fc9c4895ac564539ce867daf@huawei.com> (raw)
In-Reply-To: <f46dd846-3a30-4f0f-8513-fc843baeeef9@nvidia.com>
>
> On 2023/8/17 22:06, Stephen Hemminger wrote:
> > On Thu, 17 Aug 2023 05:06:20 +0000
> > Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com> wrote:
> >
> >> Hi Matan, Viacheslav,
> >> Tyler pointed out that the function __mlx5_hws_cnt_pool_enqueue_revert is accessing the ring private structure members
> (prod.head and prod.tail) directly. Even though ' struct rte_ring' is a public structure (mainly because the library provides inline
> functions), the structure members are considered private to the ring library. So, this needs to be corrected.
> >>
> >> It looks like the function __mlx5_hws_cnt_pool_enqueue_revert is trying to revert things that were enqueued. It is not clear to
> me why this functionality is required. Can you provide the use case for this? We can discuss possible solutions.
> > How can reverting be thread safe? Consumer could have already looked at them?
>
> Hey,
>
> In our case, this ring is SC/SP, only accessed by one thread
> (enqueue/dequeue/revert).
>
> The scenario we have "revert" is:
>
> We use ring to manager our HW objects (counter in this case) and for
> each core (thread) has "cache" (a SC/SP ring) for sake of performance.
>
> 1. Get objects from "cache" firstly, if cache is empty, we fetch a bulk
> of free objects from global ring into cache.
>
> 2. Put (free) objects also into "cache" firstly, if cache is full, we
> flush a bulk of objects into global ring in order to make some rooms in
> cache.
>
> However, this HW object cannot be immediately reused after free. It
> needs time to be reset and then can be used again.
>
> So when we flush cache, we want to keep the first enqueued objects still
> stay there because they have more chance already be reset than the
> latest enqueued objects.
>
> Only flush recently enqueued objects back into global ring, act as
> "LIFO" behavior.
>
> This is why we require "revert" enqueued objects.
>
Wouldn't then simple stack fit you better?
Something like lib/stack/rte_stack_std.h, but even without spinlock around?
next prev parent reply other threads:[~2023-08-18 9:05 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-17 5:06 Honnappa Nagarahalli
2023-08-17 14:06 ` Stephen Hemminger
2023-08-18 2:32 ` Jack Min
2023-08-18 4:30 ` Honnappa Nagarahalli
2023-08-18 5:57 ` Jack Min
2023-08-18 13:59 ` Honnappa Nagarahalli
2023-08-19 1:34 ` Jack Min
2023-08-21 6:06 ` Honnappa Nagarahalli
2023-08-21 6:56 ` Jack Min
2023-08-22 4:18 ` Honnappa Nagarahalli
2023-08-18 9:05 ` Konstantin Ananyev [this message]
2023-08-18 9:38 ` Jack Min
2023-08-19 11:57 ` Konstantin Ananyev
2023-08-20 1:41 ` Jack Min
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