Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753027AbbBEUCM (ORCPT ); Thu, 5 Feb 2015 15:02:12 -0500 Received: from mail-qc0-f174.google.com ([209.85.216.174]:36572 "EHLO mail-qc0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751540AbbBEUCJ (ORCPT ); Thu, 5 Feb 2015 15:02:09 -0500 MIME-Version: 1.0 In-Reply-To: <1423115891-3578-1-git-send-email-al.drozdov@gmail.com> References: <1423115891-3578-1-git-send-email-al.drozdov@gmail.com> From: Willem de Bruijn Date: Thu, 5 Feb 2015 12:01:38 -0800 Message-ID: Subject: Re: [PATCH] af_packet: don't pass empty blocks for PACKET_V3 To: Alexander Drozdov Cc: "David S. Miller" , Daniel Borkmann , Eric Dumazet , Al Viro , "Michael S. Tsirkin" , Network Development , linux-kernel Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2632 Lines: 60 On Wed, Feb 4, 2015 at 9:58 PM, Alexander Drozdov wrote: > Don't close an empty block on timeout. Its meaningless to > pass it to the user. Moreover, passing empty blocks wastes > CPU & buffer space increasing probability of packets > dropping on small timeouts. > > Side effect of this patch is indefinite user-space wait > in poll on idle links. But, I believe its better to set > timeout for poll(2) when needed than to get empty blocks > every millisecond when not needed. This change would break existing applications that have come to depend on the periodic signal. I don't disagree with the argument that the data ready signal should be sent only when a block is full or a timer expires and at least some data is waiting, but that is moot at this point. > > Signed-off-by: Alexander Drozdov > --- > net/packet/af_packet.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c > index 9cfe2e1..9a2f70a 100644 > --- a/net/packet/af_packet.c > +++ b/net/packet/af_packet.c > @@ -698,6 +698,10 @@ static void prb_retire_rx_blk_timer_expired(unsigned long data) > > if (pkc->last_kactive_blk_num == pkc->kactive_blk_num) { > if (!frozen) { > + if (!BLOCK_NUM_PKTS(pbd)) { > + /* An empty block. Just refresh the timer. */ > + goto refresh_timer; > + } > prb_retire_current_block(pkc, po, TP_STATUS_BLK_TMO); > if (!prb_dispatch_next_block(pkc, po)) > goto refresh_timer; > @@ -798,7 +802,11 @@ static void prb_close_block(struct tpacket_kbdq_core *pkc1, > h1->ts_last_pkt.ts_sec = last_pkt->tp_sec; > h1->ts_last_pkt.ts_nsec = last_pkt->tp_nsec; > } else { > - /* Ok, we tmo'd - so get the current time */ > + /* Ok, we tmo'd - so get the current time. > + * > + * It shouldn't really happen as we don't close empty > + * blocks. See prb_retire_rx_blk_timer_expired(). > + */ > struct timespec ts; > getnstimeofday(&ts); > h1->ts_last_pkt.ts_sec = ts.tv_sec; > -- > 1.9.1 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/