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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: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
This commit is contained in:
Gerrit Renker 2008-09-04 07:30:19 +02:00
parent a9c1656ab1
commit b8c6bcee1d
1 changed files with 25 additions and 41 deletions
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66
net/dccp/probe.c
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@ -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 (!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), ccid);
if (hctx)
printl("%d.%d.%d.%d:%u %d.%d.%d.%d:%u %d %d %d %d %u "
"%llu %llu %d\n",
NIPQUAD(inet->saddr), ntohs(inet->sport),
NIPQUAD(inet->daddr), ntohs(inet->dport), size,
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;
}