On 25.06.24 г. 15:54 ч., Chen Yu wrote:
The kernel can change spinlock behavior when running as a guest. But
this guest-friendly behavior causes performance problems on bare metal.
So there's a 'virt_spin_lock_key' static key to switch between the two
modes.
The static key is always enabled by default (run in guest mode) and
should be disabled for bare metal (and in some guests that want native
behavior).
Performance drop is reported when running encode/decode workload and
BenchSEE cache sub-workload.
Bisect points to commit ce0a1b608bfc ("x86/paravirt: Silence unused
native_pv_lock_init() function warning"). When CONFIG_PARAVIRT_SPINLOCKS
is disabled the virt_spin_lock_key is incorrectly set to true on bare
metal. The qspinlock degenerates to test-and-set spinlock, which
decrease the performance on bare metal.
Set the default value of virt_spin_lock_key to false. If booting in a VM,
enable this key. Later during the VM initialization, if other
high-efficient spinlock is preferred(paravirt-spinlock eg), the
virt_spin_lock_key is disabled accordingly. The relation is described as
below:
X86_FEATURE_HYPERVISOR Y Y Y N
CONFIG_PARAVIRT_SPINLOCKS Y Y N Y/N
PV spinlock Y N N Y/N
virt_spin_lock_key N N Y N
Fixes: ce0a1b608bfc ("x86/paravirt: Silence unused native_pv_lock_init() function warning")
Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Suggested-by: Qiuxu Zhuo <qiuxu.zhuo@xxxxxxxxx>
Suggested-by: Nikolay Borisov <nik.borisov@xxxxxxxx>
Reported-by: Prem Nath Dey <prem.nath.dey@xxxxxxxxx>
Reported-by: Xiaoping Zhou <xiaoping.zhou@xxxxxxxxx>
Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
Reviewed-by: Nikolay Borisov <nik.borisov@xxxxxxxx>
