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Commit b8c6bcee authored by Gerrit Renker's avatar Gerrit Renker
Browse files

dccp: Reduce noise in output and convert to ktime_t 



This fixes the problem that dccp_probe output can grow quite large without
apparent benefit (many identical data points), creating huge files (up to
over one Gigabyte for a few minutes' test run) which are very hard to 
post-process (in one instance it got so bad that gnuplot ate up all memory
plus swap).

The cause for the problem is that the kprobe is inserted into dccp_sendmsg(),
which can be called in a polling-mode (whenever the TX queue is full due to
congestion-control issues, EAGAIN is returned). This creates many very 
similar data points, i.e. the increase of processing time does not increase
the quality/information of the probe output.

The fix is to attach the probe to a different function -- write_xmit was
chosen since it gets called continually (both via userspace and timer);
an input-path function would stop sampling as soon as the other end stops
sending feedback.

For comparison the output file sizes for the same 20 second test
run over a lossy link:
           * before / without patch:  118   Megabytes
           * after  / with patch:       1.2 Megabytes
and there was much less noise in the output.     

To allow backward compatibility with scripts that people use, the now-unused
`size' field in the output has been replaced with the CCID identifier. This
also serves for future compatibility - support for CCID2 is work in progress
(depends on the still unfinished SRTT/RTTVAR updates).

While at it, the update to ktime_t was also performed.

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: default avatarIan McDonald <ian.mcdonald@jandi.co.nz>
parent a9c1656a

net/dccp/probe.c

+25 −41
Original line number Diff line number Diff line
@@ -46,70 +46,54 @@ static struct { 
	struct kfifo	  *fifo;

	spinlock_t	  lock;

	wait_queue_head_t wait;

	struct timespec	  tstart;

	ktime_t		  start;

} dccpw;



static void printl(const char *fmt, ...)

{

	va_list args;

	int len;

	struct timespec now;

	char tbuf[256];



	va_start(args, fmt);

	getnstimeofday(&now);



	now = timespec_sub(now, dccpw.tstart);



	len = sprintf(tbuf, "%lu.%06lu ",

		      (unsigned long) now.tv_sec,

		      (unsigned long) now.tv_nsec / NSEC_PER_USEC);

	len += vscnprintf(tbuf+len, sizeof(tbuf)-len, fmt, args);

	va_end(args);



	kfifo_put(dccpw.fifo, tbuf, len);

	wake_up(&dccpw.wait);

}



static int jdccp_sendmsg(struct kiocb *iocb, struct sock *sk,

			 struct msghdr *msg, size_t size)

static void jdccp_write_xmit(struct sock *sk)

{

	const struct inet_sock *inet = inet_sk(sk);

	struct ccid3_hc_tx_sock *hctx = NULL;

	struct timespec tv;

	char buf[256];

	int len, ccid = ccid_get_current_tx_ccid(dccp_sk(sk));



	if (ccid_get_current_tx_ccid(dccp_sk(sk)) == DCCPC_CCID3)

	if (ccid == DCCPC_CCID3)

		hctx = ccid3_hc_tx_sk(sk);



	if (port == 0 || ntohs(inet->dport) == port ||

	    ntohs(inet->sport) == port) {

		if (hctx)

			printl("%d.%d.%d.%d:%u %d.%d.%d.%d:%u %d %d %d %d %u "

			       "%llu %llu %d\n",

	if (!port || ntohs(inet->dport) == port || ntohs(inet->sport) == port) {



		tv  = ktime_to_timespec(ktime_sub(ktime_get(), dccpw.start));

		len = sprintf(buf, "%lu.%09lu %d.%d.%d.%d:%u %d.%d.%d.%d:%u %d",

			       (unsigned long)tv.tv_sec,

			       (unsigned long)tv.tv_nsec,

			       NIPQUAD(inet->saddr), ntohs(inet->sport),

			       NIPQUAD(inet->daddr), ntohs(inet->dport), size,

			       NIPQUAD(inet->daddr), ntohs(inet->dport), ccid);



		if (hctx)

			len += sprintf(buf + len, " %d %d %d %u %u %u %d",

			       hctx->s, hctx->rtt, hctx->p, hctx->x_calc,

			       hctx->x_recv >> 6, hctx->x >> 6, hctx->t_ipi);

		else

			printl("%d.%d.%d.%d:%u %d.%d.%d.%d:%u %d\n",

			       NIPQUAD(inet->saddr), ntohs(inet->sport),

			       NIPQUAD(inet->daddr), ntohs(inet->dport), size);

			       (unsigned)(hctx->x_recv >> 6),

			       (unsigned)(hctx->x >> 6), hctx->t_ipi);



		len += sprintf(buf + len, "\n");

		kfifo_put(dccpw.fifo, buf, len);

		wake_up(&dccpw.wait);

	}



	jprobe_return();

	return 0;

}



static struct jprobe dccp_send_probe = {

	.kp	= {

		.symbol_name = "dccp_sendmsg",

		.symbol_name = "dccp_write_xmit",

	},

	.entry	= jdccp_sendmsg,

	.entry	= jdccp_write_xmit,

};



static int dccpprobe_open(struct inode *inode, struct file *file)

{

	kfifo_reset(dccpw.fifo);

	getnstimeofday(&dccpw.tstart);

	dccpw.start = ktime_get();

	return 0;

}