netdev - 答复: 答复: [PATCH][v2] page_pool: handle page recycle for NUMA_NO

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Date:   Mon, 16 Dec 2019 10:57:56 +0000
From:   "Li,Rongqing" <lirongqing@...du.com>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>
CC:     Yunsheng Lin <linyunsheng@...wei.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        "jonathan.lemon@...il.com" <jonathan.lemon@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Björn Töpel <bjorn.topel@...el.com>
Subject: 答复: 答复: [PATCH][v2] page_pool: handle page recycle for NUMA_NO_NODE condition



> -----邮件原件-----
> 发件人: Ilias Apalodimas [mailto:ilias.apalodimas@...aro.org]
> 发送时间: 2019年12月16日 18:17
> 收件人: Li,Rongqing <lirongqing@...du.com>
> 抄送: Yunsheng Lin <linyunsheng@...wei.com>; Jesper Dangaard Brouer
> <brouer@...hat.com>; Saeed Mahameed <saeedm@...lanox.com>;
> jonathan.lemon@...il.com; netdev@...r.kernel.org; mhocko@...nel.org;
> peterz@...radead.org; Greg Kroah-Hartman <gregkh@...uxfoundation.org>;
> bhelgaas@...gle.com; linux-kernel@...r.kernel.org; Björn Töpel
> <bjorn.topel@...el.com>
> 主题: Re: 答复: [PATCH][v2] page_pool: handle page recycle for
> NUMA_NO_NODE condition
> 
> > > >
> > > > Simply clearing the pool->alloc.cache when calling
> > > > page_pool_update_nid() seems better.
> > > >
> > >
> > > How about the below codes, the driver can configure p.nid to any, which will
> be adjusted in NAPI polling, irq migration will not be problem, but it will add a
> check into hot path.
> >
> > We'll have to check the impact on some high speed (i.e 100gbit)
> > interface between doing anything like that. Saeed's current patch runs
> > once per NAPI. This runs once per packet. The load might be measurable.
> > The READ_ONCE is needed in case all producers/consumers run on the
> > same CPU
> 
> I meant different cpus!
> 

If no READ_ONCE, pool->p.nid will be always written and become dirty although it is unshared by multiple cpus

See Eric' patch:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=503978aca46124cd714703e180b9c8292ba50ba7

-Li 
> > right?
> >
> >
> > Thanks
> > /Ilias
> > >
> > > diff --git a/net/core/page_pool.c b/net/core/page_pool.c index
> > > a6aefe989043..4374a6239d17 100644
> > > --- a/net/core/page_pool.c
> > > +++ b/net/core/page_pool.c
> > > @@ -108,6 +108,10 @@ static struct page
> *__page_pool_get_cached(struct page_pool *pool)
> > >                 if (likely(pool->alloc.count)) {
> > >                         /* Fast-path */
> > >                         page =
> > > pool->alloc.cache[--pool->alloc.count];
> > > +
> > > +                       if (unlikely(READ_ONCE(pool->p.nid) !=
> numa_mem_id()))
> > > +                               WRITE_ONCE(pool->p.nid,
> > > + numa_mem_id());
> > > +
> > >                         return page;
> > >                 }
> > >                 refill = true;
> > > @@ -155,6 +159,10 @@ static struct page
> *__page_pool_alloc_pages_slow(struct page_pool *pool,
> > >         if (pool->p.order)
> > >                 gfp |= __GFP_COMP;
> > >
> > > +
> > > +       if (unlikely(READ_ONCE(pool->p.nid) != numa_mem_id()))
> > > +               WRITE_ONCE(pool->p.nid, numa_mem_id());
> > > +
> > >         /* FUTURE development:
> > >          *
> > >          * Current slow-path essentially falls back to single page
> > > Thanks
> > >
> > > -Li
> > > > >
> > >