From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Drozdov Subject: Re: [PATCH] af_packet: don't pass empty blocks for PACKET_V3 Date: Fri, 06 Feb 2015 09:54:21 +0300 Message-ID: <54D4651D.6060300@gmail.com> References: <1423115891-3578-1-git-send-email-al.drozdov@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: "David S. Miller" , Daniel Borkmann , Eric Dumazet , Al Viro , "Michael S. Tsirkin" , Network Development , linux-kernel , Guy Harris , Dan Collins To: Willem de Bruijn Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 05.02.2015 23:01:38 +0300 Willem de Bruijn wrote: > 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. I missed something. As pointed by Guy Harris , before the previous patch periodic signal was not delivered. The previous patch (da413eec729dae5dc by Dan Collins ) is for 3.19 kernel only. Should we care about existing 3.19-only applications? > >> 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 >>