From 0733379b512ce36ba0b10942f9597b74f579f063 Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov Date: Fri, 3 Mar 2017 14:21:41 +0100 Subject: x86/hyperv: Move TSC reading method to asm/mshyperv.h As a preparation to making Hyper-V TSC page suitable for vDSO move the TSC page reading logic to asm/mshyperv.h. While on it, do the following: - Document the reading algorithm. - Simplify the code a bit. - Add explicit READ_ONCE() to not rely on 'volatile'. - Add explicit barriers to prevent re-ordering (we need to read sequence strictly before and after) - Use mul_u64_u64_shr() instead of assembly, gcc generates a single 'mul' instruction on x86_64 anyway. [ tglx: Simplified the loop ] Signed-off-by: Vitaly Kuznetsov Cc: Stephen Hemminger Cc: Haiyang Zhang Cc: Dexuan Cui Cc: Andy Lutomirski Cc: devel@linuxdriverproject.org Cc: "K. Y. Srinivasan" Cc: virtualization@lists.linux-foundation.org Link: http://lkml.kernel.org/r/20170303132142.25595-3-vkuznets@redhat.com Signed-off-by: Thomas Gleixner --- arch/x86/hyperv/hv_init.c | 36 ++++-------------------------------- 1 file changed, 4 insertions(+), 32 deletions(-) (limited to 'arch/x86/hyperv') diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c index bb1ea58ecd7a..7f5152356a59 100644 --- a/arch/x86/hyperv/hv_init.c +++ b/arch/x86/hyperv/hv_init.c @@ -38,39 +38,11 @@ struct ms_hyperv_tsc_page *hv_get_tsc_page(void) static u64 read_hv_clock_tsc(struct clocksource *arg) { - u64 current_tick; + u64 current_tick = hv_read_tsc_page(tsc_pg); + + if (current_tick == U64_MAX) + rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick); - if (tsc_pg->tsc_sequence != 0) { - /* - * Use the tsc page to compute the value. - */ - - while (1) { - u64 tmp; - u32 sequence = tsc_pg->tsc_sequence; - u64 cur_tsc; - u64 scale = tsc_pg->tsc_scale; - s64 offset = tsc_pg->tsc_offset; - - rdtscll(cur_tsc); - /* current_tick = ((cur_tsc *scale) >> 64) + offset */ - asm("mulq %3" - : "=d" (current_tick), "=a" (tmp) - : "a" (cur_tsc), "r" (scale)); - - current_tick += offset; - if (tsc_pg->tsc_sequence == sequence) - return current_tick; - - if (tsc_pg->tsc_sequence != 0) - continue; - /* - * Fallback using MSR method. - */ - break; - } - } - rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick); return current_tick; } -- cgit v1.2.3