mirror of https://gitee.com/openkylin/linux.git
51fc97b935
After a lot of discussions with AMD it turns out that TSC on Fam10h CPUs is synchronized when the CONSTANT_TSC cpuid bit is set. Or rather that if there are ever systems where that is not true it would be their BIOS' task to disable the bit. So finally use TSC gettimeofday on Fam10h by default. Or rather it is always used now on CPUs where the AMD specific CONSTANT_TSC bit is set. This gives a nice speed bost for gettimeofday() on these systems which tends to be by far the most common v/syscall. On a Fam10h system here TSC gtod uses about 20% of the CPU time of acpi_pm based gtod(). This was measured on 32bit, on 64bit it is even better because TSC gtod() can use a vsyscall and stay in ring 3, which acpi_pm doesn't. The Intel check simply checks for CONSTANT_TSC too without hardcoding Intel vendor. This is equivalent on 64bit because all 64bit capable Intel CPUs will have CONSTANT_TSC set. On Intel there is no CPU supplied CONSTANT_TSC bit currently, but we synthesize one based on hardcoded knowledge which steppings have p-state invariant TSC. So the new logic is now: On CPUs which have the AMD specific CONSTANT_TSC bit set or on Intel CPUs which are new enough to be known to have p-state invariant TSC always use TSC based gettimeofday() Cc: lenb@kernel.org Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
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