netdev - Re: [PATCH] octeontx2-pf: Use the napi_alloc

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Message-ID: <CA+sq2CfMoOhrVz7tMkKiM3BwAgoyMj6i2RWz0JWwvpBMCO3Whg@mail.gmail.com>
Date:   Fri, 8 May 2020 10:18:27 +0530
From:   Sunil Kovvuri <sunil.kovvuri@...il.com>
To:     Kevin Hao <haokexin@...il.com>
Cc:     Linux Netdev List <netdev@...r.kernel.org>,
        Sunil Goutham <sgoutham@...vell.com>,
        Geetha sowjanya <gakula@...vell.com>,
        Subbaraya Sundeep <sbhatta@...vell.com>,
        hariprasad <hkelam@...vell.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] octeontx2-pf: Use the napi_alloc_frag() to alloc the pool buffers

On Fri, May 8, 2020 at 9:43 AM Kevin Hao <haokexin@...il.com> wrote:
>
> In the current codes, the octeontx2 uses its own method to allocate
> the pool buffers, but there are some issues in this implementation.
> 1. We have to run the otx2_get_page() for each allocation cycle and
>    this is pretty error prone. As I can see there is no invocation
>    of the otx2_get_page() in otx2_pool_refill_task(), this will leave
>    the allocated pages have the wrong refcount and may be freed wrongly.

Thanks for pointing, will fix.

> 2. It wastes memory. For example, if we only receive one packet in a
>    NAPI RX cycle, and then allocate a 2K buffer with otx2_alloc_rbuf()
>    to refill the pool buffers and leave the remain area of the allocated
>    page wasted. On a kernel with 64K page, 62K area is wasted.
>
> IMHO it is really unnecessary to implement our own method for the
> buffers allocate, we can reuse the napi_alloc_frag() to simplify
> our code.
>
> Signed-off-by: Kevin Hao <haokexin@...il.com>

Have you measured performance with and without your patch ?
I didn't use napi_alloc_frag() as it's too costly, if in one NAPI
instance driver
receives 32 pkts, then 32 calls to napi_alloc_frag() and updates to page ref
count per fragment etc are costly. When traffic rate is less then it
may not matter
much.

Thanks,
Sunil.