From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christopher Covington Subject: Re: [Qemu-devel] [kvm-unit-tests PATCHv4 3/3] arm: pmu: Add CPI checking Date: Mon, 19 Oct 2015 11:44:30 -0400 Message-ID: <56250FDE.8000008@codeaurora.org> References: <5612EDA5.9010506@redhat.com> <1444662470-13045-1-git-send-email-cov@codeaurora.org> <1444662470-13045-4-git-send-email-cov@codeaurora.org> <20151018182821.GC12158@hawk.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, wei@redhat.com, alindsay@codeaurora.org, croberts@codeaurora.org, shannon.zhao@linaro.org, alistair.francis@xilinx.com To: Andrew Jones Return-path: Received: from smtp.codeaurora.org ([198.145.29.96]:55615 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752610AbbJSPod (ORCPT ); Mon, 19 Oct 2015 11:44:33 -0400 In-Reply-To: <20151018182821.GC12158@hawk.localdomain> Sender: kvm-owner@vger.kernel.org List-ID: Hi Drew, I appreciate your feedback on these patches. On 10/18/2015 02:28 PM, Andrew Jones wrote: >> --- a/arm/pmu.c >> +++ b/arm/pmu.c >> @@ -37,6 +37,18 @@ static inline unsigned long get_pmccntr(void) >> asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r" (cycles)); >> return cycles; >> } >> + >> +static inline void loop(int i, uint32_t pmcr) >> +{ >> + uint32_t z = 0; >> + >> + asm volatile( >> + " mcr p15, 0, %[pmcr], c9, c12, 0\n" >> + " 1: subs %[i], %[i], #1\n" >> + " bgt 1b\n" >> + " mcr p15, 0, %[z], c9, c12, 0\n" >> + : [i] "+r" (i) : [pmcr] "r" (pmcr), [z] "r" (z) : "cc"); > > Assembly is always ugly, but we can do a bit better formatting with tabs > > asm volatile( > " mcr p15, 0, %[pmcr], c9, c12, 0\n" > "1: subs %[i], %[i], #1\n" > " bgt 1b\n" > " mcr p15, 0, %[z], c9, c12, 0\n" > : [i] "+r" (i) > : [pmcr] "r" (pmcr), [z] "r" (z) > : "cc"); > > Actually it can be even cleaner because you already created set_pmcr() > > set_pmcr(pmcr); > > asm volatile( > "1: subs %0, %0, #1\n" > " bgt 1b\n" > : "+r" (i) : : "cc"); > > set_pmcr(0); Is there any way to ensure that the compiler won't for example put a `mov rd, #0` between the `bgt 1b` and the `mcr , rn`? >> @@ -125,12 +147,79 @@ static bool check_cycles_increase(void) >> return true; >> } >> >> -int main(void) >> +/* >> + * Execute a known number of guest instructions. Only odd instruction counts >> + * greater than or equal to 3 are supported by the in-line assembly code. The > > Not all odd counts, right? But rather all multiples of 3? IIUC this is because > the loop is two instructions (sub + branch), and then the clearing of the pmcr > register counts as the 3rd? Clearing the PMCR doesn't happen as part of the loop, but as part of the loop exit or epilogue. total_instrs = iteration_count * loop_instrs + eipilogue_instrs total_instrs = iteration_count * 2 + 1 Thanks, Christopher Covington -- Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project