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[122.58.176.92]) by smtp.gmail.com with ESMTPSA id 124-v6sm46327734pfb.132.2018.11.13.00.24.32 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 13 Nov 2018 00:24:37 -0800 (PST) Subject: Re: [RFC PATCH 06/13] m68k: Drop ARCH_USES_GETTIMEOFFSET To: Finn Thain References: <74edaee07800f91eb416ab3e72c4670b8ef4bd4e.1541995959.git.fthain@telegraphics.com.au> Cc: Geert Uytterhoeven , Arnd Bergmann , Stephen N Chivers , Thomas Gleixner , Daniel Lezcano , John Stultz , linux-m68k , Linux Kernel Mailing List , Philip Blundell , Joshua Thompson From: Michael Schmitz Message-ID: <0054c37f-ef34-e892-ff1d-02968ab529fa@gmail.com> Date: Tue, 13 Nov 2018 21:24:30 +1300 User-Agent: Mozilla/5.0 (X11; Linux ppc; rv:45.0) Gecko/20100101 Icedove/45.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Finn, Am 13.11.2018 um 19:15 schrieb Finn Thain: > On Tue, 13 Nov 2018, Michael Schmitz wrote: > >> >>> (It appears that a QEMU-emulated Mac does not benefit from having a >>> clocksource that's more accurate than the 'jiffies' clocksource, in >>> spite of "clocksource: Switched to clocksource via1".) >> >> With the current code, kernel log timestamps have 10 ms resolution on >> Atari. Time resolution of times reported by initcall_debug is roughly 40 >> us. I'd expect that changes with falling back to jiffies only. Might be >> worth a try on QEMU Mac. > > The initcall debug output shows the same precision as my earlier tests > with userland. The VIA timer only gets updated when QEMU wants to update > it, which seems to be about every 9765 us. Hence, using the 'jiffies' > clocksource would be effectively no regression for a virtual Mac. Running a recent kernel under ARAnyM shows 40 ns resolution so the Atari hardware emulation is a little more complete. Using that for initial tests, I can confirm that timer resolution is reduced to 10ms after patch 6, and gets restored to 40ns after applying the full series (once clocksource_init runs, that is - the first part of the boot is at 10ms resolution only, a regression compared to with use of arch_gettimeoffset). Unfortunately, I can't log in at the console with all patches applied. I immediately get the 'login timeout exceeded' message. Weird... Cheers, Michael