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Date:   Fri, 8 May 2020 13:30:15 +0800
From:   Kevin Hao <>
To:     Sunil Kovvuri <>
Cc:     Linux Netdev List <>,
        Sunil Goutham <>,
        Geetha sowjanya <>,
        Subbaraya Sundeep <>,
        hariprasad <>,
        "David S. Miller" <>
Subject: Re: [PATCH] octeontx2-pf: Use the napi_alloc_frag() to alloc the
 pool buffers

On Fri, May 08, 2020 at 10:18:27AM +0530, Sunil Kovvuri wrote:
> On Fri, May 8, 2020 at 9:43 AM Kevin Hao <> 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 <>
> Have you measured performance with and without your patch ?

I will do performance compare later. But I don't think there will be measurable

> 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.

No, the page ref only be updated at the page allocation and all the space are
used. In general, the invocation of napi_alloc_frag() will not cause the update
of the page ref. So in theory, the count of updating page ref should be reduced
by using of napi_alloc_frag() compare to the current otx2 implementation.


> When traffic rate is less then it
> may not matter
> much.
> Thanks,
> Sunil.

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