| Message ID | 1487183463-882-3-git-send-email-longman@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Waiman,
[auto build test ERROR on kvm/linux-next]
[also build test ERROR on v4.10-rc8 next-20170215]
[cannot apply to tip/x86/core]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Waiman-Long/x86-kvm-Reduce-vcpu_is_preempted-overhead/20170216-033517
base: https://git.kernel.org/pub/scm/virt/kvm/kvm.git linux-next
config: i386-randconfig-h1-02160052 (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
# save the attached .config to linux build tree
make ARCH=i386
All error/warnings (new ones prefixed by >>):
In file included from include/uapi/linux/stddef.h:1:0,
from include/linux/stddef.h:4,
from include/uapi/linux/posix_types.h:4,
from include/uapi/linux/types.h:13,
from include/linux/types.h:5,
from include/uapi/linux/capability.h:16,
from include/linux/capability.h:15,
from include/linux/sched.h:15,
from include/linux/context_tracking.h:4,
from arch/x86/kernel/kvm.c:23:
arch/x86/kernel/kvm.c: In function 'kvm_spinlock_init':
>> arch/x86/kernel/kvm.c:631:6: error: 'PREEMPTED_OFFSET' undeclared (first use in this function)
!= PREEMPTED_OFFSET) || (sizeof(steal_time.preempted) != 1));
^
include/linux/compiler.h:498:19: note: in definition of macro '__compiletime_assert'
bool __cond = !(condition); \
^~~~~~~~~
include/linux/compiler.h:518:2: note: in expansion of macro '_compiletime_assert'
_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
^~~~~~~~~~~~~~~~~~~
include/linux/bug.h:54:37: note: in expansion of macro 'compiletime_assert'
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
^~~~~~~~~~~~~~~~~~
include/linux/bug.h:78:2: note: in expansion of macro 'BUILD_BUG_ON_MSG'
BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
^~~~~~~~~~~~~~~~
>> arch/x86/kernel/kvm.c:630:2: note: in expansion of macro 'BUILD_BUG_ON'
BUILD_BUG_ON((offsetof(struct kvm_steal_time, preempted)
^~~~~~~~~~~~
arch/x86/kernel/kvm.c:631:6: note: each undeclared identifier is reported only once for each function it appears in
!= PREEMPTED_OFFSET) || (sizeof(steal_time.preempted) != 1));
^
include/linux/compiler.h:498:19: note: in definition of macro '__compiletime_assert'
bool __cond = !(condition); \
^~~~~~~~~
include/linux/compiler.h:518:2: note: in expansion of macro '_compiletime_assert'
_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
^~~~~~~~~~~~~~~~~~~
include/linux/bug.h:54:37: note: in expansion of macro 'compiletime_assert'
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
^~~~~~~~~~~~~~~~~~
include/linux/bug.h:78:2: note: in expansion of macro 'BUILD_BUG_ON_MSG'
BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
^~~~~~~~~~~~~~~~
>> arch/x86/kernel/kvm.c:630:2: note: in expansion of macro 'BUILD_BUG_ON'
BUILD_BUG_ON((offsetof(struct kvm_steal_time, preempted)
^~~~~~~~~~~~
vim +/PREEMPTED_OFFSET +631 arch/x86/kernel/kvm.c
624
625 /*
626 * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
627 */
628 void __init kvm_spinlock_init(void)
629 {
> 630 BUILD_BUG_ON((offsetof(struct kvm_steal_time, preempted)
> 631 != PREEMPTED_OFFSET) || (sizeof(steal_time.preempted) != 1));
632
633 if (!kvm_para_available())
634 return;
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 85ed343..83e22c1 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -589,6 +589,7 @@ static void kvm_wait(u8 *ptr, u8 val) local_irq_restore(flags); } +#ifdef CONFIG_X86_32 __visible bool __kvm_vcpu_is_preempted(long cpu) { struct kvm_steal_time *src = &per_cpu(steal_time, cpu); @@ -597,11 +598,38 @@ __visible bool __kvm_vcpu_is_preempted(long cpu) } PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted); +#else + +extern bool __raw_callee_save___kvm_vcpu_is_preempted(long); + +/* + * Hand-optimize version for x86-64 to avoid 8 64-bit register saving and + * restoring to/from the stack. It is assumed that the preempted value + * is at an offset of 16 from the beginning of the kvm_steal_time structure + * which is verified by the BUILD_BUG_ON() macro below. + */ +#define PREEMPTED_OFFSET 16 +asm( +".pushsection .text;" +".global __raw_callee_save___kvm_vcpu_is_preempted;" +".type __raw_callee_save___kvm_vcpu_is_preempted, @function;" +"__raw_callee_save___kvm_vcpu_is_preempted:" +"movq __per_cpu_offset(,%rdi,8), %rax;" +"cmpb $0, " __stringify(PREEMPTED_OFFSET) "+steal_time(%rax);" +"setne %al;" +"ret;" +".popsection"); + +#endif + /* * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present. */ void __init kvm_spinlock_init(void) { + BUILD_BUG_ON((offsetof(struct kvm_steal_time, preempted) + != PREEMPTED_OFFSET) || (sizeof(steal_time.preempted) != 1)); + if (!kvm_para_available()) return; /* Does host kernel support KVM_FEATURE_PV_UNHALT? */
It was found when running fio sequential write test with a XFS ramdisk on a KVM guest running on a 2-socket x86-64 system, the %CPU times as reported by perf were as follows: 69.75% 0.59% fio [k] down_write 69.15% 0.01% fio [k] call_rwsem_down_write_failed 67.12% 1.12% fio [k] rwsem_down_write_failed 63.48% 52.77% fio [k] osq_lock 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted Making vcpu_is_preempted() a callee-save function has a relatively high cost on x86-64 primarily due to at least one more cacheline of data access from the saving and restoring of registers (8 of them) to and from stack as well as one more level of function call. To reduce this performance overhead, an optimized assembly version of the the __raw_callee_save___kvm_vcpu_is_preempt() function is provided for x86-64. With this patch applied on a KVM guest on a 2-socekt 16-core 32-thread system with 16 parallel jobs (8 on each socket), the aggregrate bandwidth of the fio test on an XFS ramdisk were as follows: I/O Type w/o patch with patch -------- --------- ---------- random read 8141.2 MB/s 8497.1 MB/s seq read 8229.4 MB/s 8304.2 MB/s random write 1675.5 MB/s 1701.5 MB/s seq write 1681.3 MB/s 1699.9 MB/s There are some increases in the aggregated bandwidth because of the patch. The perf data now became: 70.78% 0.58% fio [k] down_write 70.20% 0.01% fio [k] call_rwsem_down_write_failed 69.70% 1.17% fio [k] rwsem_down_write_failed 59.91% 55.42% fio [k] osq_lock 10.14% 10.14% fio [k] __kvm_vcpu_is_preempted The assembly code was verified by using a test kernel module to compare the output of C __kvm_vcpu_is_preempted() and that of assembly __raw_callee_save___kvm_vcpu_is_preempt() to verify that they matched. Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Waiman Long <longman@redhat.com> --- arch/x86/kernel/kvm.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+)