From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.tuxdriver.com (charlotte.tuxdriver.com [70.61.120.58]) by dpdk.org (Postfix) with ESMTP id C9B883B5 for ; Wed, 1 Oct 2014 13:07:09 +0200 (CEST) Received: from [2001:470:8:a08:9833:6894:f2b2:43a] (helo=localhost) by smtp.tuxdriver.com with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.63) (envelope-from ) id 1XZHqt-0007R6-AO; Wed, 01 Oct 2014 07:13:52 -0400 Date: Wed, 1 Oct 2014 07:13:46 -0400 From: Neil Horman To: Hiroshi Shimamoto Message-ID: <20141001111346.GD21151@hmsreliant.think-freely.org> References: <7F861DC0615E0C47A872E6F3C5FCDDBD02AE26C5@BPXM14GP.gisp.nec.co.jp> <20140930143242.GI2193@hmsreliant.think-freely.org> <7F861DC0615E0C47A872E6F3C5FCDDBD02AE2D37@BPXM14GP.gisp.nec.co.jp> <20141001084445.GC1204@BRICHA3-MOBL> <7F861DC0615E0C47A872E6F3C5FCDDBD02AE3BAF@BPXM14GP.gisp.nec.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7F861DC0615E0C47A872E6F3C5FCDDBD02AE3BAF@BPXM14GP.gisp.nec.co.jp> User-Agent: Mutt/1.5.23 (2014-03-12) X-Spam-Score: -2.9 (--) X-Spam-Status: No Cc: "dev@dpdk.org" , Hayato Momma Subject: Re: [dpdk-dev] [memnic PATCH v2 6/7] pmd: add branch hint in recv/xmit X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 01 Oct 2014 11:07:10 -0000 On Wed, Oct 01, 2014 at 09:12:44AM +0000, Hiroshi Shimamoto wrote: > > Subject: Re: [dpdk-dev] [memnic PATCH v2 6/7] pmd: add branch hint in recv/xmit > > > > On Tue, Sep 30, 2014 at 11:52:00PM +0000, Hiroshi Shimamoto wrote: > > > Hi, > > > > > > > Subject: Re: [dpdk-dev] [memnic PATCH v2 6/7] pmd: add branch hint in recv/xmit > > > > > > > > On Tue, Sep 30, 2014 at 11:14:40AM +0000, Hiroshi Shimamoto wrote: > > > > > From: Hiroshi Shimamoto > > > > > > > > > > To reduce instruction cache miss, add branch condition hints into > > > > > recv/xmit functions. This improves a bit performance. > > > > > > > > > > We can see performance improvements with memnic-tester. > > > > > Using Xeon E5-2697 v2 @ 2.70GHz, 4 vCPU. > > > > > size | before | after > > > > > 64 | 5.54Mpps | 5.55Mpps > > > > > 128 | 5.46Mpps | 5.44Mpps > > > > > 256 | 5.21Mpps | 5.22Mpps > > > > > 512 | 4.50Mpps | 4.52Mpps > > > > > 1024 | 3.71Mpps | 3.73Mpps > > > > > 1280 | 3.21Mpps | 3.22Mpps > > > > > 1518 | 2.92Mpps | 2.93Mpps > > > > > > > > > > Signed-off-by: Hiroshi Shimamoto > > > > > Reviewed-by: Hayato Momma > > > > > --- > > > > > pmd/pmd_memnic.c | 18 +++++++++--------- > > > > > 1 file changed, 9 insertions(+), 9 deletions(-) > > > > > > > > > > diff --git a/pmd/pmd_memnic.c b/pmd/pmd_memnic.c > > > > > index 7fc3093..875d3ea 100644 > > > > > --- a/pmd/pmd_memnic.c > > > > > +++ b/pmd/pmd_memnic.c > > > > > @@ -289,26 +289,26 @@ static uint16_t memnic_recv_pkts(void *rx_queue, > > > > > int idx, next; > > > > > struct rte_eth_stats *st = &adapter->stats[rte_lcore_id()]; > > > > > > > > > > - if (!adapter->nic->hdr.valid) > > > > > + if (unlikely(!adapter->nic->hdr.valid)) > > > > > return 0; > > > > > > > > > > pkts = bytes = errs = 0; > > > > > idx = adapter->up_idx; > > > > > for (nr = 0; nr < nb_pkts; nr++) { > > > > > p = &data->packets[idx]; > > > > > - if (p->status != MEMNIC_PKT_ST_FILLED) > > > > > + if (unlikely(p->status != MEMNIC_PKT_ST_FILLED)) > > > > > break; > > > > > /* prefetch the next area */ > > > > > next = idx; > > > > > - if (++next >= MEMNIC_NR_PACKET) > > > > > + if (unlikely(++next >= MEMNIC_NR_PACKET)) > > > > > next = 0; > > > > > rte_prefetch0(&data->packets[next]); > > > > > - if (p->len > framesz) { > > > > > + if (unlikely(p->len > framesz)) { > > > > > errs++; > > > > > goto drop; > > > > > } > > > > > mb = rte_pktmbuf_alloc(adapter->mp); > > > > > - if (!mb) > > > > > + if (unlikely(!mb)) > > > > > break; > > > > > > > > > > rte_memcpy(rte_pktmbuf_mtod(mb, void *), p->data, p->len); > > > > > @@ -350,7 +350,7 @@ static uint16_t memnic_xmit_pkts(void *tx_queue, > > > > > uint64_t pkts, bytes, errs; > > > > > uint32_t framesz = adapter->framesz; > > > > > > > > > > - if (!adapter->nic->hdr.valid) > > > > > + if (unlikely(!adapter->nic->hdr.valid)) > > > > > return 0; > > > > > > > > > > pkts = bytes = errs = 0; > > > > > @@ -360,7 +360,7 @@ static uint16_t memnic_xmit_pkts(void *tx_queue, > > > > > struct rte_mbuf *sg; > > > > > void *ptr; > > > > > > > > > > - if (pkt_len > framesz) { > > > > > + if (unlikely(pkt_len > framesz)) { > > > > > errs++; > > > > > break; > > > > > } > > > > > @@ -379,7 +379,7 @@ retry: > > > > > goto retry; > > > > > } > > > > > > > > > > - if (idx != ACCESS_ONCE(adapter->down_idx)) { > > > > > + if (unlikely(idx != ACCESS_ONCE(adapter->down_idx))) { > > > > Why are you using ACCESS_ONCE here? Or for that matter, anywhere else in this > > > > PMD? The whole idea of the ACCESS_ONCE macro is to assign a value to a variable > > > > once and prevent it from getting reloaded from memory at a later time, this is > > > > exactly contrary to that, both in the sense that you're explicitly reloading the > > > > same variable multiple times, and that you're using it as part of a comparison > > > > operation, rather than an asignment operation > > > > > > ACCESS_ONCE prevents compiler optimization and ensures load from memory. > > > There could be multiple threads which read/write that index. > > > We should compare the value previous and the current value in memory. > > > In that reason, I use ACCESS_ONCE macro to get value in the memory. > > > > Should you not just make the variable volatile? That's the normal way to > > guarantee reads from memory and prevent the compiler caching things in > > registers. > > We don't want always accessing to memory, it could cause performance degradation. > Like linux kernel, I use it in the place only we really load from memory. > Thats not true at all. Every single read of adapter->down_idx in memnic_xmit_pkts() is wrapped in a ACCESS_ONCE call. Theres no difference in doing that and just declaring a volitile variable and pointing it to &adapter->down_idx (save for the increased legibility of the code) Neil > thanks, > Hiroshi > > > > > /Bruce > > > > > > > > thanks, > > > Hiroshi > > > > > > > > > > > Neil > > > >