From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752246AbcAEKvy (ORCPT ); Tue, 5 Jan 2016 05:51:54 -0500 Received: from foss.arm.com ([217.140.101.70]:57444 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751603AbcAEKvu (ORCPT ); Tue, 5 Jan 2016 05:51:50 -0500 Subject: Re: [PATCH v5 03/11] arm-cci: Group writes to counter To: Mark Rutland References: <1451908490-2615-1-git-send-email-suzuki.poulose@arm.com> <1451908490-2615-4-git-send-email-suzuki.poulose@arm.com> <20160104190353.GC17127@leverpostej> Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, arm@kernel.org, punit.agrawal@arm.com, peterz@infradead.org From: "Suzuki K. Poulose" Message-ID: <568BA043.2020302@arm.com> Date: Tue, 5 Jan 2016 10:51:47 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <20160104190353.GC17127@leverpostej> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/01/16 19:03, Mark Rutland wrote: > On Mon, Jan 04, 2016 at 11:54:42AM +0000, Suzuki K. Poulose wrote: >> Add a helper to group the writes to PMU counter, this will be >> used to delay setting the event period to pmu::pmu_enable() >> >> +/* Write a value to a given set of counters */ >> +static void __pmu_write_counters(struct cci_pmu *cci_pmu, unsigned long *mask, u32 value) >> +{ >> + int i; >> + >> + for_each_set_bit(i, mask, cci_pmu->num_cntrs) >> + __pmu_write_counter(cci_pmu, value, i); >> +} > > I don't understand this as-is. Why do all the counters have the same > value? The only value we write to the counters is the period. This routine writes a given value to a set of counters specified by the mask (not to be confused with the PMU->hw_events->mask). This will help to group the writes to the counters, especially since preparatory steps to write to a single counter itself is costly. So, we do all the preparation only once for a batch of counters. The other option is to use hw_events->prev_count (which should be set before calling the function) for each counter specified in the mask. I am fine with either of the two. > >> +static void __maybe_unused >> +pmu_write_counters(struct cci_pmu *cci_pmu, unsigned long *mask, u32 value) >> +{ >> + __pmu_write_counters(cci_pmu, mask, value); >> +} > > Why are these not just one function for now? Yes, this could be just one function for now, until we introduce the hooks. This was a written to avoid another refactoring in the later patch. Thanks Suzuki