From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH v4 01/13] Linux RDMA Core Changes Date: Wed, 3 Jan 2007 21:33:24 +0200 Message-ID: <20070103193324.GD29003@mellanox.co.il> References: <1167851839.4187.36.camel@stevo-desktop> Reply-To: "Michael S. Tsirkin" Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org, Roland Dreier , linux-kernel@vger.kernel.org, openib-general@openib.org Return-path: To: Steve Wise Content-Disposition: inline In-Reply-To: <1167851839.4187.36.camel@stevo-desktop> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org > 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? -- MST