[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen master] xen/x86: Drop unnecessary barriers
commit 6abb6f092e0b7035d0155607f8cb194ca9663712 Author: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> AuthorDate: Fri Dec 2 15:00:41 2016 +0000 Commit: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> CommitDate: Wed Jan 3 13:02:54 2018 +0000 xen/x86: Drop unnecessary barriers x86's current implementation of wmb() is a compiler barrier. As a result, the only change in this patch is to remove an mfence instruction from cpuidle_disable_deep_cstate(). None of these barriers serve any purpose. They are not synchronising with remote cpus, and their compiler-barrier properties are not needed for correctness purposes. Furthermore, these wmb()'s specifically do not want to turn into sfence instructions in future changes where wmb()'s implementation is corrected. Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> Acked-by: Jan Beulich <jbeulich@xxxxxxxx> --- xen/arch/x86/acpi/cpu_idle.c | 2 -- xen/arch/x86/cpu/mcheck/mce.c | 3 --- xen/arch/x86/crash.c | 3 --- xen/arch/x86/smpboot.c | 2 -- 4 files changed, 10 deletions(-) diff --git a/xen/arch/x86/acpi/cpu_idle.c b/xen/arch/x86/acpi/cpu_idle.c index 884ee32..cb1c5da 100644 --- a/xen/arch/x86/acpi/cpu_idle.c +++ b/xen/arch/x86/acpi/cpu_idle.c @@ -1341,8 +1341,6 @@ void cpuidle_disable_deep_cstate(void) max_cstate = 1; } - mb(); - hpet_disable_legacy_broadcast(); } diff --git a/xen/arch/x86/cpu/mcheck/mce.c b/xen/arch/x86/cpu/mcheck/mce.c index df0106e..a8c287d 100644 --- a/xen/arch/x86/cpu/mcheck/mce.c +++ b/xen/arch/x86/cpu/mcheck/mce.c @@ -86,7 +86,6 @@ static x86_mce_vector_t _machine_check_vector = unexpected_machine_check; void x86_mce_vector_register(x86_mce_vector_t hdlr) { _machine_check_vector = hdlr; - wmb(); } /* Call the installed machine check handler for this CPU setup. */ @@ -385,8 +384,6 @@ mcheck_mca_logout(enum mca_source who, struct mca_banks *bankmask, mcabank_clear(i); else if ( who == MCA_MCE_SCAN && need_clear ) mcabanks_set(i, clear_bank); - - wmb(); } if ( mig && errcnt > 0 ) diff --git a/xen/arch/x86/crash.c b/xen/arch/x86/crash.c index 82535c4..8d74258 100644 --- a/xen/arch/x86/crash.c +++ b/xen/arch/x86/crash.c @@ -146,9 +146,6 @@ static void nmi_shootdown_cpus(void) write_atomic((unsigned long *)__va(__pa(&exception_table[TRAP_nmi])), (unsigned long)&do_nmi_crash); - /* Ensure the new callback function is set before sending out the NMI. */ - wmb(); - smp_send_nmi_allbutself(); msecs = 1000; /* Wait at most a second for the other cpus to stop */ diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c index 0e585b3..7b97ff8 100644 --- a/xen/arch/x86/smpboot.c +++ b/xen/arch/x86/smpboot.c @@ -361,7 +361,6 @@ void start_secondary(void *unused) spin_debug_enable(); set_cpu_sibling_map(cpu); notify_cpu_starting(cpu); - wmb(); /* * We need to hold vector_lock so there the set of online cpus @@ -377,7 +376,6 @@ void start_secondary(void *unused) local_irq_enable(); mtrr_ap_init(); - wmb(); startup_cpu_idle_loop(); } -- generated by git-patchbot for /home/xen/git/xen.git#master _______________________________________________ Xen-changelog mailing list Xen-changelog@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/xen-changelog
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