netdev - Re: [RFC PATCH net-next] Introducing lockless cache built on top of slab allocator

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Date:   Tue, 21 Sep 2021 10:48:40 +0900
From:   Kangmin Park <l4stpr0gr4m@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexander Lobakin <alobakin@...me>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Guillaume Nault <gnault@...hat.com>,
        Vasily Averin <vvs@...tuozzo.com>,
        Cong Wang <cong.wang@...edance.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH net-next] Introducing lockless cache built on top of
 slab allocator

2021년 9월 21일 (화) 오전 5:50, Jakub Kicinski <kuba@...nel.org>님이 작성:
>
> On Tue, 21 Sep 2021 02:47:13 +0900 Kangmin Park wrote:
> > It is just introducing and proof of concept.
> > The patch code is based on other RFC patches. So, the code is not
> > correct yet, it is just simple proof of concept.
> >
> > Recently block layer implemented percpu, lockless cache on the top
> > of slab allocator. It can be used for IO polling.
> >
> > Link: https://lwn.net/Articles/868070/
> > Link: https://www.spinics.net/lists/linux-block/msg71964.html
> >
> > It gained some IOPS increase (performance increased by about 10%
> > on the block layer).
> >
> > And there are attempts to implement the percpu, lockless cache.
> >
> > Link: https://lore.kernel.org/linux-mm/20210920154816.31832-1-42.hyeyoo@gmail.com/T/#u
> >
> > If this cache is implemented successfully,
> > how about use this cache to allocate skb instead of kmem_cache_alloc_bulk()
> > in napi_skb_cache_get()?
> >
> > I want your comment/opinion.
>
> Please take a look at skb cache in struct napi_alloc_cache.
> That should be your target here.
>

Oh, thanks for the advice.
I'll send you a v2 patch to replace/improve napi_alloc_cache
when progress is made in implementing the lockless cache.

Best Regards,
Kangmin Park

> > Signed-off-by: Kangmin Park <l4stpr0gr4m@...il.com>
> > ---
> >  net/core/skbuff.c | 14 +++++++++-----
> >  1 file changed, 9 insertions(+), 5 deletions(-)
> >
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index 7c2ab27fcbf9..f9a9deca423d 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -170,11 +170,15 @@ static struct sk_buff *napi_skb_cache_get(void)
> >       struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
> >       struct sk_buff *skb;
> >
> > -     if (unlikely(!nc->skb_count))
> > -             nc->skb_count = kmem_cache_alloc_bulk(skbuff_head_cache,
> > -                                                   GFP_ATOMIC,
> > -                                                   NAPI_SKB_CACHE_BULK,
> > -                                                   nc->skb_cache);
> > +     if (unlikely(!nc->skb_count)) {
> > +             /* kmem_cache_alloc_cached should be changed to return the size of
> > +              * the allocated cache
> > +              */
> > +             nc->skb_cache = kmem_cache_alloc_cached(skbuff_head_cache,
> > +                                                     GFP_ATOMIC | SLB_LOCKLESS_CACHE);
> > +             nc->skb_count = this_cpu_ptr(skbuff_head_cache)->size;
> > +     }
> > +
> >       if (unlikely(!nc->skb_count))
> >               return NULL;
> >