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

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Message-ID: <CA+sq2CfmFaQ1=8m6vBOD6d_uoez2yU7KrAP1JUMo_nJbe=9_6g@mail.gmail.com>
Date:   Fri, 8 May 2020 13:08:13 +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 11:00 AM Kevin Hao <haokexin@...il.com> wrote:
>
> On Fri, May 08, 2020 at 10:18:27AM +0530, Sunil Kovvuri wrote:
> > 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 will do performance compare later. But I don't think there will be measurable
> difference.
>
> > 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.
>

Okay, it seems i misunderstood it. Have tested this patch.
Tested-by: Sunil Goutham <sgoutham@...vell.com>