linux - linux

	Commit message (Collapse)	Author	Age	Files	Lines
*	powerpc/pseries: Fix hcall tracing recursion in pv queued spinlocks	Nicholas Piggin	2021-05-12	1	-3/+19
\| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \|	The paravit queued spinlock slow path adds itself to the queue then calls pv_wait to wait for the lock to become free. This is implemented by calling H_CONFER to donate cycles. When hcall tracing is enabled, this H_CONFER call can lead to a spin lock being taken in the tracing code, which will result in the lock to be taken again, which will also go to the slow path because it queues behind itself and so won't ever make progress. An example trace of a deadlock: __pv_queued_spin_lock_slowpath trace_clock_global ring_buffer_lock_reserve trace_event_buffer_lock_reserve trace_event_buffer_reserve trace_event_raw_event_hcall_exit __trace_hcall_exit plpar_hcall_norets_trace __pv_queued_spin_lock_slowpath trace_clock_global ring_buffer_lock_reserve trace_event_buffer_lock_reserve trace_event_buffer_reserve trace_event_raw_event_rcu_dyntick rcu_irq_exit irq_exit __do_irq call_do_irq do_IRQ hardware_interrupt_common_virt Fix this by introducing plpar_hcall_norets_notrace(), and using that to make SPLPAR virtual processor dispatching hcalls by the paravirt spinlock code. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20210508101455.1578318-2-npiggin@gmail.com
*	powerpc: Fix build error in paravirt.h	Michal Suchanek	2021-01-31	1	-0/+1
\| \| \| \| \| \| \| \| \| \| \| \| \| \| \|	./arch/powerpc/include/asm/paravirt.h:83:44: error: implicit declaration of function 'smp_processor_id'; did you mean 'raw_smp_processor_id'? smp_processor_id is defined in linux/smp.h but it is not included. The build error happens only when the patch is applied to 5.3 kernel but it only works by chance in mainline. Fixes: ca3f969dcb11 ("powerpc/paravirt: Use is_kvm_guest() in vcpu_is_preempted()") Signed-off-by: Michal Suchanek <msuchanek@suse.de> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20210120132838.15589-1-msuchanek@suse.de
*	powerpc/paravirt: Use is_kvm_guest() in vcpu_is_preempted()	Srikar Dronamraju	2020-12-03	1	-0/+18
\| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \|	If its a shared LPAR but not a KVM guest, then see if the vCPU is related to the calling vCPU. On PowerVM, only cores can be preempted. So if one vCPU is a non-preempted state, we can decipher that all other vCPUs sharing the same core are in non-preempted state. Performance results: $ perf stat -r 5 -a perf bench sched pipe -l 10000000 (lesser time is better) powerpc/next 35,107,951.20 msec cpu-clock # 255.898 CPUs utilized ( +- 0.31% ) 23,655,348 context-switches # 0.674 K/sec ( +- 3.72% ) 14,465 cpu-migrations # 0.000 K/sec ( +- 5.37% ) 82,463 page-faults # 0.002 K/sec ( +- 8.40% ) 1,127,182,328,206 cycles # 0.032 GHz ( +- 1.60% ) (66.67%) 78,587,300,622 stalled-cycles-frontend # 6.97% frontend cycles idle ( +- 0.08% ) (50.01%) 654,124,218,432 stalled-cycles-backend # 58.03% backend cycles idle ( +- 1.74% ) (50.01%) 834,013,059,242 instructions # 0.74 insn per cycle # 0.78 stalled cycles per insn ( +- 0.73% ) (66.67%) 132,911,454,387 branches # 3.786 M/sec ( +- 0.59% ) (50.00%) 2,890,882,143 branch-misses # 2.18% of all branches ( +- 0.46% ) (50.00%) 137.195 +- 0.419 seconds time elapsed ( +- 0.31% ) powerpc/next + patchset 29,981,702.64 msec cpu-clock # 255.881 CPUs utilized ( +- 1.30% ) 40,162,456 context-switches # 0.001 M/sec ( +- 0.01% ) 1,110 cpu-migrations # 0.000 K/sec ( +- 5.20% ) 62,616 page-faults # 0.002 K/sec ( +- 3.93% ) 1,430,030,626,037 cycles # 0.048 GHz ( +- 1.41% ) (66.67%) 83,202,707,288 stalled-cycles-frontend # 5.82% frontend cycles idle ( +- 0.75% ) (50.01%) 744,556,088,520 stalled-cycles-backend # 52.07% backend cycles idle ( +- 1.39% ) (50.01%) 940,138,418,674 instructions # 0.66 insn per cycle # 0.79 stalled cycles per insn ( +- 0.51% ) (66.67%) 146,452,852,283 branches # 4.885 M/sec ( +- 0.80% ) (50.00%) 3,237,743,996 branch-misses # 2.21% of all branches ( +- 1.18% ) (50.01%) 117.17 +- 1.52 seconds time elapsed ( +- 1.30% ) This is around 14.6% improvement in performance. Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Acked-by: Waiman Long <longman@redhat.com> [mpe: Fold in performance results from cover letter] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20201202050456.164005-5-srikar@linux.vnet.ibm.com
*	powerpc/pseries: Implement paravirt qspinlocks for SPLPAR	Nicholas Piggin	2020-07-26	1	-0/+28
\| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \| \|	This implements the generic paravirt qspinlocks using H_PROD and H_CONFER to kick and wait. This uses an un-directed yield to any CPU rather than the directed yield to a pre-empted lock holder that paravirtualised simple spinlocks use, that requires no kick hcall. This is something that could be investigated and improved in future. Performance results can be found in the commit which added queued spinlocks. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Waiman Long <longman@redhat.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20200724131423.1362108-5-npiggin@gmail.com
*	powerpc/pseries: Move some PAPR paravirt functions to their own file	Nicholas Piggin	2020-07-26	1	-0/+59
	These functions will be used by the queued spinlock implementation, and may be useful elsewhere too, so move them out of spinlock.h. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: Waiman Long <longman@redhat.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20200724131423.1362108-2-npiggin@gmail.com