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SubjectRe: [PATCH] 2.5.21 Nonlinear CPU support
On Wed, 12 Jun 2002 02:26:41 -0700 (PDT)
"David S. Miller" <davem@redhat.com> wrote:

> From: Rusty Russell <rusty@rustcorp.com.au>
> Date: Wed, 12 Jun 2002 16:58:23 +1000
>
> In message <20020611.021043.04190747.davem@redhat.com> you write:
> > And remember, it's the anal "every microoptimization at all costs"
> > people that keep the kernel sane and from running out of control bloat
> > wise.
>
> But it also gave us crap like net/ipv4/route.c:ip_rt_acct_read() 8(
>
> That's far from being an attempt optimization :-)

I was giving you the benifit of the doubt, that both the design (binary
data from /proc) and the code (#ifdef, cpu_logical_map(0), and "256"
sprinkled everywhere) were some insane attempt at speed, rather that
a demonstration of sheer programming idiocy.

I stand corrected 8). This papers over the damage:

diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5.21/net/ipv4/route.c working-2.5.21-ipacct/net/ipv4/route.c
--- linux-2.5.21/net/ipv4/route.c Mon May 13 12:00:40 2002
+++ working-2.5.21-ipacct/net/ipv4/route.c Thu Jun 13 14:33:41 2002
@@ -2418,10 +2418,15 @@
#ifdef CONFIG_NET_CLS_ROUTE
struct ip_rt_acct *ip_rt_acct;

+/* This code sucks. But you should have seen it before! --RR */
+
+/* IP route accounting ptr for this logical cpu number. */
+#define IP_RT_ACCT_CPU(i) (ip_rt_acct + cpu_logical_map(i) * 256)
+
static int ip_rt_acct_read(char *buffer, char **start, off_t offset,
int length, int *eof, void *data)
{
- *start = buffer;
+ unsigned int i;

if ((offset & 3) || (length & 3))
return -EIO;
@@ -2430,35 +2435,18 @@
length = sizeof(struct ip_rt_acct) * 256 - offset;
*eof = 1;
}
- if (length > 0) {
- u32 *dst = (u32*)buffer;
- u32 *src = (u32*)(((u8*)ip_rt_acct) + offset);
-
- memcpy(dst, src, length);
-
-#ifdef CONFIG_SMP
- if (smp_num_cpus > 1 || cpu_logical_map(0) != 0) {
- int i;
- int cnt = length / 4;
-
- for (i = 0; i < smp_num_cpus; i++) {
- int cpu = cpu_logical_map(i);
- int k;

- if (cpu == 0)
- continue;
-
- src = (u32*)(((u8*)ip_rt_acct) + offset +
- cpu * 256 * sizeof(struct ip_rt_acct));
+ /* Copy first cpu. */
+ *start = buffer;
+ memcpy(buffer, IP_RT_ACCT_CPU(0), length);

- for (k = 0; k < cnt; k++)
- dst[k] += src[k];
- }
- }
-#endif
- return length;
+ /* Add the other cpus in, one int at a time */
+ for (i = 1; i < smp_num_cpus; i++) {
+ unsigned int j;
+ for (j = 0; j < length/4; j++)
+ ((u32*)buffer)[j] += ((u32*)IP_RT_ACCT_CPU(i))[j];
}
- return 0;
+ return length;
}
#endif

--
there are those who do and those who hang on and you don't see too
many doers quoting their contemporaries. -- Larry McVoy
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