Re: [PATCH v4 01/13] Linux RDMA Core Changes
From: Steve Wise
Date: Wed Jan 03 2007 - 15:20:53 EST
On Wed, 2007-01-03 at 21:33 +0200, Michael S. Tsirkin wrote:
> > Without extra param (1000 iterations in cycles):
> > ave 101.283 min 91 max 247
> > With extra param (1000 iterations in cycles):
> > ave 103.311 min 91 max 221
>
> A 2% hit then. Not huge, but 0 either.
>
> > Convert cycles to ns (3466.727 MHz CPU):
> >
> > Without: 101.283 / 3466.727 = .02922us == 29.22ns
> > With: 103.311 / 3466.727 = .02980us == 29.80ns
> >
> > So I measure a .58ns average increase for passing in the additional
> > parameter.
>
> That depends on CPU speed though. Percentage is likely to be more universal.
>
> > Here is a snipit of the test:
> >
> > spin_lock_irq(&lock);
> > do_gettimeofday(&start_tv);
> > for (i=0; i<1000; i++) {
> > cycles_start[i] = get_cycles();
> > ib_req_notify_cq(cb->cq, IB_CQ_NEXT_COMP);
> > cycles_stop[i] = get_cycles();
> > }
> > do_gettimeofday(&stop_tv);
> > spin_unlock_irq(&lock);
> >
> > if (stop_tv.tv_usec < start_tv.tv_usec) {
> > stop_tv.tv_usec += 1000000;
> > stop_tv.tv_sec -= 1;
> > }
> >
> > for (i=0; i < 1000; i++) {
> > cycles_t v = cycles_stop[i] - cycles_start[i];
> > sum += v;
> > if (v > max)
> > max = v;
> > if (min == 0 || v < min)
> > min = v;
> > }
> >
> > printk(KERN_ERR PFX "FOO delta sec %lu usec %lu sum %llu min %llu max %llu\n",
> > stop_tv.tv_sec - start_tv.tv_sec,
> > stop_tv.tv_usec - start_tv.tv_usec,
> > (unsigned long long)sum, (unsigned long long)min,
> > (unsigned long long)max);
>
> Good job, the test looks good, thanks.
>
> So what does this tell you?
> To me it looks like there's a measurable speed difference,
> and so we should find a way (e.g. what I proposed) to enable chelsio userspace
> without adding overhead to other low level drivers or indeed chelsio kernel level code.
>
> What do you think? Roland?
>
I think having a 2nd function to set the udata seems onerous.
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