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[82.252.144.192]) by smtp.googlemail.com with ESMTPSA id 91sm5782778wrl.20.2021.03.02.05.01.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 Mar 2021 05:01:25 -0800 (PST) Subject: Re: [PATCH v2 07/10] clocksource/drivers/hyper-v: Handle vDSO differences inline To: Michael Kelley , Stephen Hemminger , KY Srinivasan , "wei.liu@kernel.org" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "hpa@zytor.com" , "arnd@arndb.de" , "linux-hyperv@vger.kernel.org" Cc: "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "linux-arch@vger.kernel.org" References: <1614561332-2523-1-git-send-email-mikelley@microsoft.com> <1614561332-2523-8-git-send-email-mikelley@microsoft.com> <42dc252a-b09a-afeb-6792-9b77669c16e9@linaro.org> From: Daniel Lezcano Message-ID: Date: Tue, 2 Mar 2021 14:01:24 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On 02/03/2021 02:29, Michael Kelley wrote: > From: Daniel Lezcano Sent: Monday, March 1, 2021 4:22 AM >> >> On 01/03/2021 02:15, Michael Kelley wrote: >>> While the driver for the Hyper-V Reference TSC and STIMERs is architecture >>> neutral, vDSO is implemented for x86/x64, but not for ARM64. Current code >>> calls into utility functions under arch/x86 (and coming, under arch/arm64) >>> to handle the difference. >>> >>> Change this approach to handle the difference inline based on whether >>> VDSO_CLOCK_MODE_HVCLOCK is present. The new approach removes code under >>> arch/* since the difference is tied more to the specifics of the Linux >>> implementation than to the architecture. >>> >>> No functional change. >> >> A suggestion below >> >> >>> Signed-off-by: Michael Kelley >>> Reviewed-by: Boqun Feng >>> --- >>> arch/x86/include/asm/mshyperv.h | 4 ---- >>> drivers/clocksource/hyperv_timer.c | 10 ++++++++-- >>> 2 files changed, 8 insertions(+), 6 deletions(-) >>> >>> diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c >>> index c73c127..5e5e08aa 100644 >>> --- a/drivers/clocksource/hyperv_timer.c >>> +++ b/drivers/clocksource/hyperv_timer.c >>> @@ -372,7 +372,9 @@ static void resume_hv_clock_tsc(struct clocksource *arg) >>> >>> static int hv_cs_enable(struct clocksource *cs) >> >> static __maybe_unused int hv_cs_enable(struct clocksource *cs) >> >>> { >>> - hv_enable_vdso_clocksource(); >>> +#ifdef VDSO_CLOCKMODE_HVCLOCK >>> + vclocks_set_used(VDSO_CLOCKMODE_HVCLOCK); >>> +#endif >>> return 0; >>> } >>> >>> @@ -385,6 +387,11 @@ static int hv_cs_enable(struct clocksource *cs) >>> .suspend= suspend_hv_clock_tsc, >>> .resume = resume_hv_clock_tsc, >>> .enable = hv_cs_enable, >>> +#ifdef VDSO_CLOCKMODE_HVCLOCK >>> + .vdso_clock_mode = VDSO_CLOCKMODE_HVCLOCK, >>> +#else >>> + .vdso_clock_mode = VDSO_CLOCKMODE_NONE, >>> +#endif >> >> #ifdef VDSO_CLOCKMODE_HVCLOCK >> .enable = hv_cs_enable, >> .vdso_clock_mode = VDSO_CLOCKMODE_HVCLOCK, >> #else >> .vdso_clock_mode = VDSO_CLOCKMODE_NONE, >> #endif >> > > Is there any particular benefit (that I might not be recognizing) > to having the .enable function be NULL vs. a function that > does nothing? I can see the handful of places where the > .enable function is invoked, and there doesn't seem to be > much difference. > > In any case, I have no problem with making the change in > a v3 of the patch set. It is just coding style, it allows to remove a #ifdef in the code. -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog