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kprof: don't downsample the pc

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Kprof rounded the pc to 8 byte boundaries in order to save memory.
With x86 instruction rounding this can lead to some pretty misleading
results.

With the old rounding kpdata was ~680kb for a pc64 kernel, with this
change we use ~5.4M (8x) and considering we only allocate when we
first attach this seems reasonable.
This commit is contained in:
Jacob Moody 2025-01-05 00:26:52 +00:00
parent 4de9d8a511
commit 28465682cf
3 changed files with 5 additions and 11 deletions
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7
sys/man/3/kprof
View file

@ -24,10 +24,9 @@ The size of the file depends on the size of kernel text.
The first count
holds the total number of clock ticks during profiling;
the second the number of ticks that occurred while the kernel
was running. The rest each hold the number of ticks
the kernel program counter was within the
corresponding 8-byte range of kernel text, starting from the base
of kernel text.
was running. The rest each hold the number of total ticks
the kernel spent at any one program counter, indexed by
their offset from the minimum kernel text address.
.PP
The file
.B kpctl

4
sys/src/9/port/devkprof.c
View file

@ -6,7 +6,6 @@
#include "../port/error.h"
#define LRES 3 /* log of PC resolution */
#define SZ 4 /* sizeof of count cell; well known as 4 */
struct
@ -46,7 +45,6 @@ _kproftimer(uintptr pc)
kprof.buf[0] += TK2MS(1);
if(kprof.minpc<=pc && pc<kprof.maxpc){
pc -= kprof.minpc;
pc >>= LRES;
kprof.buf[pc] += TK2MS(1);
}else
kprof.buf[1] += TK2MS(1);
@ -68,7 +66,7 @@ kprofattach(char *spec)
/* allocate when first used */
kprof.minpc = KTZERO;
kprof.maxpc = (uintptr)etext;
kprof.nbuf = (kprof.maxpc-kprof.minpc) >> LRES;
kprof.nbuf = kprof.maxpc-kprof.minpc;
n = kprof.nbuf*SZ;
if(kprof.buf == 0) {
kprof.buf = xalloc(n);

5
sys/src/cmd/kprof.c
View file

@ -3,8 +3,6 @@
#include <bio.h>
#include <mach.h>
#define PCRES 8
struct COUNTER
{
char *name; /* function name */
@ -82,7 +80,7 @@ main(int argc, char *argv[])
data = malloc(d->length);
if(data == 0)
error(1, "malloc");
if(read(fd, data, d->length) < 0)
if(readn(fd, data, d->length) != d->length)
error(1, "text read");
close(fd);
for(i=0; i<n; i++)
@ -112,7 +110,6 @@ main(int argc, char *argv[])
if (!textsym(&s, i)) /* get next symbol */
break;
s.value -= tbase;
s.value /= PCRES;
sum = 0;
while (j < n && j < s.value)
sum += data[j++];