* bh_lru_install
@ 2004-07-24 0:03 David S. Miller
2004-07-27 23:06 ` bh_lru_install Andrew Morton
0 siblings, 1 reply; 4+ messages in thread
From: David S. Miller @ 2004-07-24 0:03 UTC (permalink / raw)
To: linux-kernel
[-- Attachment #1: Type: text/plain, Size: 862 bytes --]
So I was doing some profiling of memcpy() calls to try and tune
the UltraSPARC-III memcpy a little more, and you wouldn't believe
what was at the top of the list during a kernel build :-)
It's bh_lru_install. On a 64-bit system every time the local
cpu's lru->bh[0] doesn't match 'bh' we do a 64-byte memcpy()
from the stack into the lru->bh[] array.
It shouldn't be too hard to make the code just work without
an on-stack copy, shuffling the lru->bh[] array entries
directly.
For the curious, attached is profiling output after a full kernel
build on this box. I basically rigged it such that the per-cpu
timer profiling stuff didn't touch prof_buffer, and every
memcpy() call recorded __builtin_return_address(0). It also
keeps alignment and length distribution information accessible
via proc. Example dumps and that debugging patch are attached
too.
[-- Attachment #2: memcpy_stats.diff --]
[-- Type: text/plain, Size: 4967 bytes --]
===== arch/sparc64/kernel/setup.c 1.54 vs edited =====
--- 1.54/arch/sparc64/kernel/setup.c 2004-06-27 00:19:38 -07:00
+++ edited/arch/sparc64/kernel/setup.c 2004-07-23 15:58:47 -07:00
@@ -32,6 +32,7 @@
#include <linux/interrupt.h>
#include <linux/cpu.h>
#include <linux/initrd.h>
+#include <linux/profile.h>
#include <asm/segment.h>
#include <asm/system.h>
@@ -714,3 +715,80 @@
}
subsys_initcall(topology_init);
+
+static u64 memcpy_lens[256 + 1];
+static u64 src_align[64];
+static u64 dst_align[64];
+
+extern __kernel_size_t __real_memcpy(void *, const void *, __kernel_size_t);
+
+__kernel_size_t __memcpy(void *dst, const void *src, __kernel_size_t len)
+{
+ memcpy_lens[(len <= 256) ? len : 256]++;
+ src_align[((long)src) & 63]++;
+ dst_align[((long)dst) & 63]++;
+
+ if (prof_buffer) {
+ unsigned long pc;
+
+ pc = (unsigned long) __builtin_return_address(0);
+ pc -= (unsigned long) _stext;
+ pc >>= prof_shift;
+ if (pc >= prof_len)
+ pc = prof_len - 1;
+ atomic_inc((atomic_t *)&prof_buffer[pc]);
+ }
+
+ return __real_memcpy(dst, src, len);
+}
+
+static int show_memcpy_lens(struct seq_file *m, void *__unused)
+{
+ int i;
+
+ for (i = 0; i <= 256; i++)
+ seq_printf(m, "[%3d]: %lu\n", i, memcpy_lens[i]);
+
+ return 0;
+}
+
+struct seq_operations memcpy_lens_op = {
+ .start =c_start,
+ .next = c_next,
+ .stop = c_stop,
+ .show = show_memcpy_lens,
+};
+
+static int show_memcpy_src_align(struct seq_file *m, void *__unused)
+{
+ int i;
+
+ for (i = 0; i < 64; i++)
+ seq_printf(m, "[%2d]: %lu\n", i, src_align[i]);
+
+ return 0;
+}
+
+struct seq_operations src_align_op = {
+ .start =c_start,
+ .next = c_next,
+ .stop = c_stop,
+ .show = show_memcpy_src_align,
+};
+
+static int show_memcpy_dst_align(struct seq_file *m, void *__unused)
+{
+ int i;
+
+ for (i = 0; i < 64; i++)
+ seq_printf(m, "[%2d]: %lu\n", i, dst_align[i]);
+
+ return 0;
+}
+
+struct seq_operations dst_align_op = {
+ .start =c_start,
+ .next = c_next,
+ .stop = c_stop,
+ .show = show_memcpy_dst_align,
+};
===== arch/sparc64/kernel/time.c 1.53 vs edited =====
--- 1.53/arch/sparc64/kernel/time.c 2004-05-07 07:17:21 -07:00
+++ edited/arch/sparc64/kernel/time.c 2004-07-23 15:09:34 -07:00
@@ -443,11 +443,12 @@
void sparc64_do_profile(struct pt_regs *regs)
{
+#if 0
unsigned long pc = regs->tpc;
unsigned long o7 = regs->u_regs[UREG_RETPC];
-
+#endif
profile_hook(regs);
-
+#if 0
if (user_mode(regs))
return;
@@ -480,6 +481,7 @@
pc = prof_len - 1;
atomic_inc((atomic_t *)&prof_buffer[pc]);
}
+#endif
}
static irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs * regs)
===== arch/sparc64/lib/VIScopy.S 1.6 vs edited =====
--- 1.6/arch/sparc64/lib/VIScopy.S 2004-02-10 21:34:37 -08:00
+++ edited/arch/sparc64/lib/VIScopy.S 2004-07-23 15:05:25 -07:00
@@ -306,11 +306,11 @@
.globl __memcpy_begin
__memcpy_begin:
- .globl __memcpy
- .type __memcpy,@function
+ .globl __real_memcpy
+ .type __real_memcpy,@function
memcpy_private:
-__memcpy:
+__real_memcpy:
memcpy: mov ASI_P, asi_src ! IEU0 Group
brnz,pt %o2, __memcpy_entry ! CTI
mov ASI_P, asi_dest ! IEU1
===== fs/proc/proc_misc.c 1.103 vs edited =====
--- 1.103/fs/proc/proc_misc.c 2004-06-24 01:55:46 -07:00
+++ edited/fs/proc/proc_misc.c 2004-07-23 15:05:25 -07:00
@@ -270,6 +270,42 @@
.release = seq_release,
};
+extern struct seq_operations memcpy_lens_op;
+static int memcpy_lens_open(struct inode *inode, struct file *file)
+{
+ return seq_open(file, &memcpy_lens_op);
+}
+static struct file_operations proc_memcpy_lens_operations = {
+ .open = memcpy_lens_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+};
+
+extern struct seq_operations src_align_op;
+static int src_align_open(struct inode *inode, struct file *file)
+{
+ return seq_open(file, &src_align_op);
+}
+static struct file_operations proc_src_align_operations = {
+ .open = src_align_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+};
+
+extern struct seq_operations dst_align_op;
+static int dst_align_open(struct inode *inode, struct file *file)
+{
+ return seq_open(file, &dst_align_op);
+}
+static struct file_operations proc_dst_align_operations = {
+ .open = dst_align_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+};
+
extern struct seq_operations vmstat_op;
static int vmstat_open(struct inode *inode, struct file *file)
{
@@ -671,6 +707,9 @@
if (entry)
entry->proc_fops = &proc_kmsg_operations;
create_seq_entry("cpuinfo", 0, &proc_cpuinfo_operations);
+ create_seq_entry("memcpy_lens", 0, &proc_memcpy_lens_operations);
+ create_seq_entry("src_align", 0, &proc_src_align_operations);
+ create_seq_entry("dst_align", 0, &proc_dst_align_operations);
create_seq_entry("partitions", 0, &proc_partitions_operations);
create_seq_entry("stat", 0, &proc_stat_operations);
create_seq_entry("interrupts", 0, &proc_interrupts_operations);
[-- Attachment #3: memcpy_lens.txt --]
[-- Type: text/plain, Size: 2476 bytes --]
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[-- Attachment #4: src_align.txt --]
[-- Type: text/plain, Size: 657 bytes --]
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[-- Attachment #5: dst_align.txt --]
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: bh_lru_install
2004-07-24 0:03 bh_lru_install David S. Miller
@ 2004-07-27 23:06 ` Andrew Morton
2004-07-27 23:41 ` bh_lru_install David S. Miller
2004-07-28 0:15 ` bh_lru_install David S. Miller
0 siblings, 2 replies; 4+ messages in thread
From: Andrew Morton @ 2004-07-27 23:06 UTC (permalink / raw)
To: David S. Miller; +Cc: linux-kernel
"David S. Miller" <davem@redhat.com> wrote:
>
> So I was doing some profiling of memcpy() calls to try and tune
> the UltraSPARC-III memcpy a little more, and you wouldn't believe
> what was at the top of the list during a kernel build :-)
>
> It's bh_lru_install. On a 64-bit system every time the local
> cpu's lru->bh[0] doesn't match 'bh' we do a 64-byte memcpy()
> from the stack into the lru->bh[] array.
Well I said it was dopey-but-simple ;)
> It shouldn't be too hard to make the code just work without
> an on-stack copy, shuffling the lru->bh[] array entries
> directly.
Yup, that plus making it a ringbuffer maybe.
But I don't recall seeing bh_lru_install() standing out on profiles. I
expect that when the system is working hard we're averaging nearly zero
cache misses in that copy. Do you really think it is worth optimising?
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: bh_lru_install
2004-07-27 23:06 ` bh_lru_install Andrew Morton
@ 2004-07-27 23:41 ` David S. Miller
2004-07-28 0:15 ` bh_lru_install David S. Miller
1 sibling, 0 replies; 4+ messages in thread
From: David S. Miller @ 2004-07-27 23:41 UTC (permalink / raw)
To: Andrew Morton; +Cc: linux-kernel
On Tue, 27 Jul 2004 16:06:17 -0700
Andrew Morton <akpm@osdl.org> wrote:
> But I don't recall seeing bh_lru_install() standing out on profiles. I
> expect that when the system is working hard we're averaging nearly zero
> cache misses in that copy. Do you really think it is worth optimising?
On a full kernel build after a fresh boot, that memcpy() executes
approximately 400K times on my sparc64 boxes.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: bh_lru_install
2004-07-27 23:06 ` bh_lru_install Andrew Morton
2004-07-27 23:41 ` bh_lru_install David S. Miller
@ 2004-07-28 0:15 ` David S. Miller
1 sibling, 0 replies; 4+ messages in thread
From: David S. Miller @ 2004-07-28 0:15 UTC (permalink / raw)
To: Andrew Morton; +Cc: linux-kernel
On Tue, 27 Jul 2004 16:06:17 -0700
Andrew Morton <akpm@osdl.org> wrote:
> > It shouldn't be too hard to make the code just work without
> > an on-stack copy, shuffling the lru->bh[] array entries
> > directly.
>
> Yup, that plus making it a ringbuffer maybe.
It seems implementable using two roving indexes, one for
reading and one for writing. So it's just like the existing
code sans the on-stack+memcpy stuff :-)
Do you see any logic errors in this new code below?
static void bh_lru_install(struct buffer_head *bh)
{
struct buffer_head *e = NULL;
struct bh_lru *lru;
check_irqs_on();
bh_lru_lock();
lru = &__get_cpu_var(bh_lrus);
if ((e = lru->bhs[0]) != bh) {
int rd_idx, wr_idx;
wr_idx = 0;
get_bh(bh);
lru->bhs[wr_idx++] = bh;
for (rd_idx = 1; rd_idx < BH_LRU_SIZE; rd_idx++) {
struct buffer_head *nxt = lru->bhs[rd_idx];
if (e != NULL)
lru->bhs[wr_idx++] = e;
e = nxt;
if (e == bh) {
__brelse(e);
e = NULL;
} else if (e == NULL)
break;
}
while (wr_idx < BH_LRU_SIZE)
lru->bhs[wr_idx++] = NULL;
}
bh_lru_unlock();
if (e)
__brelse(e);
}
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2004-07-28 0:17 UTC | newest]
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2004-07-28 0:15 ` bh_lru_install David S. Miller
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