Hello, On Wed, Aug 23, 2023 at 07:06:07AM +0200, Mateusz Guzik wrote: > To start I figured I'm going to bench about as friendly case as it gets > -- statically linked *separate* binaries all doing execve in a loop. > > I borrowed the bench from here: > http://apollo.backplane.com/DFlyMisc/doexec.c > > $ cc -static -O2 -o static-doexec doexec.c > $ ./static-doexec $(nproc) > > It prints a result every second. > > My test box is temporarily only 26 cores and even at this scale I run > into massive lock contention stemming from back-to-back calls to > percpu_counter_init (and _destroy later). > > While not a panacea, one simple thing to do here is to batch these ops. > Since the term "batching" is already used in the file, I decided to > refer to it as "grouping" instead. > > Even if this code could be patched to dodge these counters, I would > argue a high-traffic alloc/free consumer is only a matter of time so it > makes sense to facilitate it. > > With the fix I get an ok win, to quote from the commit: > > Even at a very modest scale of 26 cores (ops/s): > > before: 133543.63 > > after: 186061.81 (+39%) > > While with the patch these allocations remain a significant problem, > the primary bottleneck shifts to: > > __pv_queued_spin_lock_slowpath+1 > _raw_spin_lock_irqsave+57 > folio_lruvec_lock_irqsave+91 > release_pages+590 > tlb_batch_pages_flush+61 > tlb_finish_mmu+101 > exit_mmap+327 > __mmput+61 > begin_new_exec+1245 > load_elf_binary+712 > bprm_execve+644 > do_execveat_common.isra.0+429 > __x64_sys_execve+50 > do_syscall_64+46 > entry_SYSCALL_64_after_hwframe+110 > > I intend to do more work on the area to mostly sort it out, but I would > not mind if someone else took the hammer to folio. :) > > With this out of the way I'll be looking at some form of caching to > eliminate these allocs as a problem. > > v3: > - fix !CONFIG_SMP build > - drop the backtrace from fork commit message > > v2: > - force bigger alignment on alloc > - rename "counters" to "nr_counters" and pass prior to lock key > - drop {}'s for single-statement loops > > > Mateusz Guzik (2): > pcpcntr: add group allocation/free > fork: group allocation of per-cpu counters for mm struct > > include/linux/percpu_counter.h | 39 ++++++++++++++++++---- > kernel/fork.c | 14 ++------ > lib/percpu_counter.c | 61 +++++++++++++++++++++++----------- > 3 files changed, 77 insertions(+), 37 deletions(-) > > -- > 2.41.0 > I've applied both to percpu#for-6.6. Thanks, Dennis
