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SubjectRe: netpoll/netconsole minor tweaks

On Thu, 18 Sep 2003, Alan Cox wrote:

> On Iau, 2003-09-18 at 17:48, Chris Wright wrote:
> > > <pedant>
> > > should be cpu_relax();
> > > </pedant>
> >
> > Hrm, there's many spots that aren't using it. What's the benefit, less
> > power consumption? Is it worth a patch to convert other things over?
>
> It speeds up hyperthreading CPUs by letting them know that this
> paticular thread is waiting for stuff (sched_yield for silicon)
>

Does that mean that it would be benneficial to do something like this in
for example eepro100.c ??

diff -up linux-2.6.0-test5-orig/drivers/net/eepro100.c
linux-2.6.0-test5/drivers/net/eepro100.c
--- linux-2.6.0-test5-orig/drivers/net/eepro100.c 2003-09-08 21:50:09.000000000 +0200
+++ linux-2.6.0-test5/drivers/net/eepro100.c 2003-09-19 01:03:19.000000000 +0200
@@ -913,9 +913,11 @@ static void do_slow_command(struct net_d

for (wait = 0; wait <= 100; wait++)
if (inb(cmd_ioaddr) == 0) return;
- for (; wait <= 20000; wait++)
+ for (; wait <= 20000; wait++) {
if (inb(cmd_ioaddr) == 0) return;
else udelay(1);
+ cpu_relax();
+ }
printk(KERN_ERR "Command %4.4x was not accepted after %d polls!"
" Current status %8.8x.\n",
cmd, wait, inl(dev->base_addr + SCBStatus));


or maybe even take it to the extreme like


diff -up linux-2.6.0-test5-orig/drivers/net/eepro100.c
linux-2.6.0-test5/drivers/net/eepro100.c
--- linux-2.6.0-test5-orig/drivers/net/eepro100.c 2003-09-08 21:50:09.000000000 +0200
+++ linux-2.6.0-test5/drivers/net/eepro100.c 2003-09-19 01:07:50.000000000 +0200
@@ -902,20 +902,25 @@ static void do_slow_command(struct net_d
{
long cmd_ioaddr = dev->base_addr + SCBCmd;
int wait = 0;
- do
+ do {
if (inb(cmd_ioaddr) == 0) break;
- while(++wait <= 200);
+ cpu_relax();
+ } while(++wait <= 200);
if (wait > 100)
printk(KERN_ERR "Command %4.4x never accepted (%d
polls)!\n",
inb(cmd_ioaddr), wait);

outb(cmd, cmd_ioaddr);

- for (wait = 0; wait <= 100; wait++)
+ for (wait = 0; wait <= 100; wait++) {
if (inb(cmd_ioaddr) == 0) return;
- for (; wait <= 20000; wait++)
+ cpu_relax();
+ }
+ for (; wait <= 20000; wait++) {
if (inb(cmd_ioaddr) == 0) return;
else udelay(1);
+ cpu_relax();
+ }
printk(KERN_ERR "Command %4.4x was not accepted after %d polls!"
" Current status %8.8x.\n",
cmd, wait, inl(dev->base_addr + SCBStatus));

How short/long waits are we talking about before it is benneficial to be
calling cpu_relax() ?


Kind regards,

Jesper Juhl <jju@dif.dk>
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