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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hblDq-00060V-3G; Fri, 14 Jun 2019 12:22:22 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hblAt-0002EY-CB for linux-arm-kernel@lists.infradead.org; Fri, 14 Jun 2019 12:19:25 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4E2DA3EF; Fri, 14 Jun 2019 05:19:18 -0700 (PDT) Received: from [192.168.1.18] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C24183F246; Fri, 14 Jun 2019 05:19:15 -0700 (PDT) Subject: Re: [PATCH v6 00/19] Unify vDSOs across more architectures To: Thomas Gleixner References: <20190530141531.43462-1-vincenzo.frascino@arm.com> From: Vincenzo Frascino Message-ID: <6f3bcd07-6eb4-53d6-d209-de42396a4ee2@arm.com> Date: Fri, 14 Jun 2019 13:19:58 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190614_051919_511427_5F5342FC X-CRM114-Status: GOOD ( 17.51 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch , Shuah Khan , Arnd Bergmann , Huw Davies , Catalin Marinas , Daniel Lezcano , Will Deacon , linux-mips@vger.kernel.org, Ralf Baechle , Linux Kernel Mailing List , Paul Burton , "open list:KERNEL SELFTEST FRAMEWORK" , Rasmus Villemoes , Russell King , Dmitry Safonov <0x7f454c46@gmail.com>, Mark Salyzyn , Peter Collingbourne , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 6/14/19 1:16 PM, Thomas Gleixner wrote: > On Tue, 4 Jun 2019, Vincenzo Frascino wrote: >> On 31/05/2019 09:46, Arnd Bergmann wrote: >>> One open question I touched in my review is whether we want to >>> have a vdso version of clock_getres() in all architectures or not. >>> I'd prefer to leave it out because there is very little advantage to >>> it over the system call (the results don't change at runtime and >>> can easily be cached by libc if performance ever matters), and >>> it takes up a small amount of memory for the implementation. >>> >> >> I thought about it and I ended up with what proposed in this patchset mainly for >> symmetry across all the architectures since in the end they use the same common >> code. >> >> It seems also that there is some performance impact (i.e.): >> >> clock-getres-monotonic: libc(system call): 296 nsec/call >> clock-getres-monotonic: libc(vdso): 5 nsec/call > > clock_getres() is usually not a hot path operation. > >> I agree with you though when you say that caching it in the libc is a >> possibility to overcome the performance impact. >> >>> We shouldn't just need it for consistency because all callers >>> would require implementing a fallback to the system call >>> anyway, to deal with old kernels. > > libc has the fallback already. Let's aim for 1:1 replacement of the > architecture code first and then add the extra bits in separate patches. > Ok, thanks Thomas, I will split the patches accordingly. > Thanks, > > tglx > -- Regards, Vincenzo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel