From: Daniel Lezcano <redacted> Sent: Monday, March 1, 2021 6:25 AM

On 01/03/2021 02:15, Michael Kelley wrote:

quoted

While the Hyper-V Reference TSC code is architecture neutral, the
pv_ops.time.sched_clock() function is implemented for x86/x64, but not
for ARM64. Current code calls a utility function under arch/x86 (and
coming, under arch/arm64) to handle the difference.

Change this approach to handle the difference inline based on whether
GENERIC_SCHED_CLOCK 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>
---

[ ... ]

quoted

+/*
+ * Reference to pv_ops must be inline so objtool
+ * detection of noinstr violations can work correctly.
+ */
+static __always_inline void hv_setup_sched_clock(void *sched_clock)
+{
+#ifdef CONFIG_GENERIC_SCHED_CLOCK
+	/*
+	 * We're on an architecture with generic sched clock (not x86/x64).
+	 * The Hyper-V sched clock read function returns nanoseconds, not
+	 * the normal 100ns units of the Hyper-V synthetic clock.
+	 */
+	sched_clock_register(sched_clock, 64, NSEC_PER_SEC);
+#else
+#ifdef CONFIG_PARAVIRT
+	/* We're on x86/x64 *and* using PV ops */
+	pv_ops.time.sched_clock = sched_clock;
+#endif
+#endif
+}

Please refer to:

Documentation/process/coding-style.rst

Section 21)

[ ... ]

Prefer to compile out entire functions, rather than portions of
functions or portions of expressions.

[ ... ]

OK.  I'll rework the #ifdef in v3 of the patch set.  Is the following
the preferred approach?

#ifdef CONFIG_GENERIC_SCHED_CLOCK
static __always_inline void hv_setup_sched_clock(void *sched_clock)
{
	sched_clock_register(sched_clock, 64 NSEC_PER_SEC);
}
#else
#ifdef CONFIG_PARAVIRT
static __always_inline void hv_setup_sched_clock(void *sched_clock)
{
	pv_ops.time.sched_clock = sched_clock:
}
#else
static __always_inline void hv_setup_sched_clock(void *sched_clock) {}
#endif
#endif

Michael