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Hacks for measuring interrupt latency. Interrupt latency can be

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measured accurately for periodic interrupts provided the interrupts
don't need to be serviced very quickly to keep their period almost
constant.  sio output interrupts have this property (interrupt service
can be delayed for up to 1 character time without the period changing).

This is non-optional and undocumented so that it can be added and
removed easily.  It has no significant effect unless it is enabled by
hacking on a variable using a debugger.  Hardclock and statclock interrupts
would work even better for this, at least on i386's, provided their
interrupt handlers are fast (as they are in -current but not in -stable
or in my version of -current).
This commit is contained in:
Bruce Evans 2002-03-31 06:49:38 +00:00
parent c007b10217
commit e968c4ef3c
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=93466
1 changed files with 42 additions and 2 deletions
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44
sys/dev/sio/sio.c
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@ -71,6 +71,7 @@
#include <sys/rman.h>
#include <sys/timetc.h>
#include <sys/timepps.h>
#include <sys/uio.h>
#include <isa/isavar.h>
@ -1676,6 +1677,39 @@ siointr(arg)
#endif /* COM_MULTIPORT */
}
static struct timespec siots[8192];
static int siotso;
static int volatile siotsunit = -1;
static int
sysctl_siots(SYSCTL_HANDLER_ARGS)
{
char buf[128];
long long delta;
size_t len;
int error, i;
for (i = 1; i < siotso; i++) {
delta = (long long)(siots[i].tv_sec - siots[i - 1].tv_sec) *
1000000000 +
(siots[i].tv_nsec - siots[i - 1].tv_nsec);
len = sprintf(buf, "%lld\n", delta);
if (delta >= 110000)
len += sprintf(buf + len - 1, ": *** %ld.%09ld\n",
(long)siots[i].tv_sec, siots[i].tv_nsec);
if (i == siotso - 1)
buf[len - 1] = '\0';
error = SYSCTL_OUT(req, buf, len);
if (error != 0)
return (error);
uio_yield();
}
return (0);
}
SYSCTL_PROC(_machdep, OID_AUTO, siots, CTLTYPE_STRING | CTLFLAG_RD,
0, 0, sysctl_siots, "A", "sio timestamps");
static void
siointr1(com)
struct com_s *com;
@ -1845,7 +1879,7 @@ if (com->iptr - com->ibuf == 8)
if (line_status & LSR_TXRDY
&& com->state >= (CS_BUSY | CS_TTGO | CS_ODEVREADY)) {
ioptr = com->obufq.l_head;
if (com->tx_fifo_size > 1) {
if (com->tx_fifo_size > 1 && com->unit != siotsunit) {
u_int ocount;
ocount = com->obufq.l_tail - ioptr;
@ -1858,6 +1892,11 @@ if (com->iptr - com->ibuf == 8)
} else {
outb(com->data_port, *ioptr++);
++com->bytes_out;
if (com->unit == siotsunit) {
nanouptime(&siots[siotso]);
siotso = (siotso + 1) %
(sizeof siots / sizeof siots[0]);
}
}
com->obufq.l_head = ioptr;
if (COM_IIR_TXRDYBUG(com->flags)) {
@ -2206,7 +2245,8 @@ comparam(tp, t)
* interrupt disablement times in other parts of the system,
* without producing silo overflow errors.
*/
com->fifo_image = t->c_ospeed <= 4800
com->fifo_image = com->unit == siotsunit ? 0
: t->c_ospeed <= 4800
? FIFO_ENABLE : FIFO_ENABLE | FIFO_RX_MEDH;
#ifdef COM_ESP
/*