netdev - Re: [PATCH v4 01/13] Linux RDMA Core Changes

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Message-Id: <1167855618.4187.65.camel@stevo-desktop>
Date:	Wed, 03 Jan 2007 14:20:18 -0600
From:	Steve Wise <swise@...ngridcomputing.com>
To:	"Michael S. Tsirkin" <mst@...lanox.co.il>
Cc:	netdev@...r.kernel.org, Roland Dreier <rdreier@...co.com>,
	linux-kernel@...r.kernel.org, openib-general@...nib.org
Subject: Re: [PATCH  v4 01/13] Linux RDMA Core Changes

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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