This patch against 2.4.0-test5-pre3 provides per-cpu system call counters
(for arch/i386 only so far), and exports them in /proc/interrupts. I'm
interested if anyone thinks this is useful or plain stupid, and/or if
anyone familiar with assembler for other archs wants to make similar
changes [note: this patch follow's Keith's recently posted patch which
also changed include/asm-i386/hardirq.h].
Lots of due care to avoid any performance degradation like syscall overhead,
SMP cacheline pingpong, etc. The changes use one of the spare fields
in irq_stat (which is cacheline aligned), and require a single additional
instruction to the ret_from_sys_call code path. Testing reveals no
statistically significant degradation in performance, i.e. on our
dual-cpu-PIII/550 system :
=== 2.2.4-test5 WITHOUT syscall acct ===
one process spinning in getpid
1816913 calls/second
two processes spinning in getpid:
1780061 calls/second
1778278 calls/second
clean kernel compile
210.310u 13.820s 3:43.81 100.1% 0+0k 0+0io 302915pf+0w
210.470u 14.090s 3:43.48 100.4% 0+0k 0+0io 302915pf+0w
=== 2.2.4-test5 WITH syscall acct ===
one process spinning in getpid
1815879 calls/second
two processes spinning in getpid:
1768717 calls/second
1763654 calls/second
clean kernel compile
207.460u 14.160s 3:40.83 100.3% 0+0k 0+0io 302915pf+0w
207.800u 14.300s 3:37.38 102.1% 0+0k 0+0io 302915pf+0w
The new /proc/interrupts looks like this:
icy 53% cat /proc/interrupts
CPU0 CPU1
0: 89722 99730 IO-APIC-edge timer
1: 2 0 IO-APIC-edge keyboard
2: 0 0 XT-PIC cascade
4: 168 162 IO-APIC-edge serial
13: 1 0 XT-PIC fpu
15: 1 3 IO-APIC-edge ide1
19: 27408 27300 IO-APIC-level aic7xxx, aic7xxx
21: 13432 13948 IO-APIC-level eth0
NMI: 189327 189327
LOC: 189299 189289
ERR: 0
SYS: 130768636 69891376 system calls
thanks
-- Mark Goodwin
SGI Engineering
---------------
--- linux/include/asm-i386/hardirq.h.orig Thu Jul 20 09:38:50 2000
+++ linux/include/asm-i386/hardirq.h Thu Jul 20 09:35:26 2000
@@ -9,7 +9,8 @@
unsigned int __local_irq_count;
unsigned int __local_bh_count;
unsigned int __nmi_counter;
- unsigned int __pad[5];
+ unsigned int __syscall_counter; /* this is updated in entry.S */
+ unsigned int __pad[4];
} ____cacheline_aligned irq_cpustat_t;
extern irq_cpustat_t irq_stat [NR_CPUS];
--- linux/arch/i386/kernel/entry.S.orig Thu Jul 20 09:39:21 2000
+++ linux/arch/i386/kernel/entry.S Thu Jul 20 09:34:44 2000
@@ -206,9 +206,11 @@
#ifdef CONFIG_SMP
movl processor(%ebx),%eax
shll $5,%eax
+ incl SYMBOL_NAME(irq_stat)+12(,%eax) # irq_stat.__syscall_counter
movl SYMBOL_NAME(softirq_state)(,%eax),%ecx
testl SYMBOL_NAME(softirq_state)+4(,%eax),%ecx
#else
+ incl SYMBOL_NAME(irq_stat)+12 # irq_stat.__syscall_counter
movl SYMBOL_NAME(softirq_state),%ecx
testl SYMBOL_NAME(softirq_state)+4,%ecx
#endif
--- linux/arch/i386/kernel/irq.c.orig Thu Jul 20 09:39:41 2000
+++ linux/arch/i386/kernel/irq.c Thu Jul 20 09:34:44 2000
@@ -170,6 +170,13 @@
p += sprintf(p, "\n");
#endif
p += sprintf(p, "ERR: %10lu\n", irq_err_count);
+
+ p += sprintf(p, "SYS: ");
+ for (j = 0; j < smp_num_cpus; j++)
+ p += sprintf(p, "%10u ",
+ irq_stat[cpu_logical_map(j)].__syscall_counter);
+ p += sprintf(p, " %14s\n", "system calls");
+
return p - buf;
}
-
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