RE: [PATCH] net/pcap: reduce time for stopping device

["Zhou, YidingX" <yidingx.zhou@intel.com>]

> -----Original Message-----
> From: Ferruh Yigit <ferruh.yigit@xilinx.com>
> Sent: Thursday, August 25, 2022 6:09 PM
> To: Zhou, YidingX <yidingx.zhou@intel.com>; dev@dpdk.org
> Cc: Zhang, Qi Z <qi.z.zhang@intel.com>; stable@dpdk.org
> Subject: Re: [PATCH] net/pcap: reduce time for stopping device
> 
> On 8/25/2022 8:20 AM, Yiding Zhou wrote:
> > The pcap file will be synchronized to the disk when stopping the device.
> > It takes a long time if the file is large that would cause the 'detach
> > sync request' timeout when the device is closed under multi-process
> > scenario.
> >
> > This commit fixes the issue by performing synchronization in Tx path
> >
> > Fixes: 4c173302c307 ("pcap: add new driver")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Yiding Zhou <yidingx.zhou@intel.com>
> > ---
> >   drivers/net/pcap/pcap_ethdev.c | 18 ++++++++++++++++--
> >   1 file changed, 16 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/pcap/pcap_ethdev.c
> > b/drivers/net/pcap/pcap_ethdev.c index ec29fd6bc5..52eafa5674 100644
> > --- a/drivers/net/pcap/pcap_ethdev.c
> > +++ b/drivers/net/pcap/pcap_ethdev.c
> > @@ -3,7 +3,7 @@
> >    * Copyright(c) 2014 6WIND S.A.
> >    * All rights reserved.
> >    */
> > -
> > +#include <unistd.h>
> >   #include <time.h>
> >
> >   #include <pcap.h>
> > @@ -38,6 +38,8 @@
> >
> >   #define RTE_PMD_PCAP_MAX_QUEUES 16
> >
> > +#define ETH_PCAP_SYNC_THRESHOLD 0x20000000
> > +
> >   static char errbuf[PCAP_ERRBUF_SIZE];
> >   static struct timespec start_time;
> >   static uint64_t start_cycles;
> > @@ -47,6 +49,8 @@ static uint8_t iface_idx;
> >   static uint64_t timestamp_rx_dynflag;
> >   static int timestamp_dynfield_offset = -1;
> >
> > +RTE_DEFINE_PER_LCORE(uint64_t, _pcap_cached_bytes);
> > +
> >   struct queue_stat {
> >   	volatile unsigned long pkts;
> >   	volatile unsigned long bytes;
> > @@ -144,6 +148,16 @@ static struct rte_eth_link pmd_link = {
> >
> >   RTE_LOG_REGISTER_DEFAULT(eth_pcap_logtype, NOTICE);
> >
> > +static inline void
> > +pcap_dumper_data_sync(pcap_dumper_t *dumper, uint32_t bytes) {
> > +	RTE_PER_LCORE(_pcap_cached_bytes) += bytes;
> > +	if (unlikely(RTE_PER_LCORE(_pcap_cached_bytes) >
> ETH_PCAP_SYNC_THRESHOLD)) {
> > +		if (!fdatasync(fileno(pcap_dump_file(dumper))))
> > +			RTE_PER_LCORE(_pcap_cached_bytes) = 0;
> > +	}
> > +}
> > +
> >   static struct queue_missed_stat*
> >   queue_missed_stat_update(struct rte_eth_dev *dev, unsigned int qid)
> >   {
> > @@ -421,7 +435,7 @@ eth_pcap_tx_dumper(void *queue, struct rte_mbuf
> **bufs, uint16_t nb_pkts)
> >   	 * process stops and to make sure the pcap file is actually written,
> >   	 * we flush the pcap dumper within each burst.
> >   	 */
> > -	pcap_dump_flush(dumper);
> > +	pcap_dumper_data_sync(dumper, tx_bytes);
> 
> 'pcap_dump_flush()' should be doing the same thing, to write buffer to file,
> isn't it working?
> 
> Can you check the return value of the 'pcap_dump_flush()' API, I wonder if it
> keeps failing, for some reason?
> 

'pcap_dump_flush()' returns 0 each time without error, it calls 'fflush()' to flush userspace buffers to kernel buffers, not disk. 'fdatasync()' to ensure data is written to disk.

> >   	dumper_q->tx_stat.pkts += num_tx;
> >   	dumper_q->tx_stat.bytes += tx_bytes;
> >   	dumper_q->tx_stat.err_pkts += nb_pkts - num_tx;