Re: [PATCH v3 07/10] clocksource/drivers/hyper-v: Handle vDSO differences inline

On 08/03/2021 14:49, Michael Kelley wrote:

From: Michael Kelley <redacted> Sent: Tuesday, March 2, 2021 3:07 PM

quoted

From: Daniel Lezcano <redacted> Sent: Tuesday, March 2, 2021 2:14 PM

quoted

On 02/03/2021 22:38, Michael Kelley wrote:

quoted

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.

Signed-off-by: Michael Kelley <redacted>
Reviewed-by: Boqun Feng <redacted>
---
 arch/x86/include/asm/mshyperv.h    |  4 ----
 drivers/clocksource/hyperv_timer.c | 10 ++++++++--
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index c10dd1c..4f566db 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h

@@ -27,10 +27,6 @@ static inline u64 hv_get_register(unsigned int reg)
 	return value;
 }

-#define hv_set_clocksource_vdso(val) \
-	((val).vdso_clock_mode = VDSO_CLOCKMODE_HVCLOCK)
-#define hv_enable_vdso_clocksource() \
-	vclocks_set_used(VDSO_CLOCKMODE_HVCLOCK);
 #define hv_get_raw_timer() rdtsc_ordered()

 /*

diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
index c73c127..06984fa 100644
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c

@@ -370,11 +370,13 @@ static void resume_hv_clock_tsc(struct clocksource *arg)
 	hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr);
 }

+#ifdef VDSO_CLOCKMODE_HVCLOCK
 static int hv_cs_enable(struct clocksource *cs)
 {
-	hv_enable_vdso_clocksource();
+	vclocks_set_used(VDSO_CLOCKMODE_HVCLOCK);
 	return 0;
 }
+#endif

We had a confusion here. The suggestion was to remove the #ifdef here
and add the __maybe_unused annotation to the function.

I wondered if maybe that's what you were getting at with your
most recent comments.  But the code doesn't compile on ARM64
with __maybe_unused instead of the #ifdef because
VDSO_CLOCKMODE_HVCLOCK is undefined.

Michael

Daniel -- any additional comments/feedback?  Getting your Ack on
this patch should be the last step to wrap up the patch series.

It would have been nice to simplify those #ifdef but I don't see a
straightforward change for that... :(

Acked-by: Daniel Lezcano <redacted>



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