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McKenney" To: "Joel Fernandes (Google)" Cc: linux-kernel@vger.kernel.org, max.byungchul.park@gmail.com, byungchul.park@lge.com, Davidlohr Bueso , Josh Triplett , kernel-team@android.com, kernel-team@lge.com, Lai Jiangshan , Mathieu Desnoyers , Rao Shoaib , rcu@vger.kernel.org, Steven Rostedt Subject: Re: [PATCH RFC v1 2/2] rcuperf: Add kfree_rcu performance Tests Message-ID: <20190807002915.GV28441@linux.ibm.com> Reply-To: paulmck@linux.ibm.com References: <20190806212041.118146-1-joel@joelfernandes.org> <20190806212041.118146-2-joel@joelfernandes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190806212041.118146-2-joel@joelfernandes.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-06_11:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908070001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 06, 2019 at 05:20:41PM -0400, Joel Fernandes (Google) wrote: > This test runs kfree_rcu in a loop to measure performance of the new > kfree_rcu, with and without patch. > > To see improvement, run with boot parameters: > rcuperf.kfree_loops=2000 rcuperf.kfree_alloc_num=100 rcuperf.perf_type=kfree > > Without patch, test runs in 6.9 seconds. > With patch, test runs in 6.1 seconds (+13% improvement) > > If it is desired to run the test but with the traditional (non-batched) > kfree_rcu, for example to compare results, then you could pass along the > rcuperf.kfree_no_batch=1 boot parameter. You lost me on this one. You ran two runs, with rcuperf.kfree_no_batch=1 and without? Or you ran this patch both with and without the earlier patch, and could have run with the patch and rcuperf.kfree_no_batch=1? If the latter, it would be good to try all three. > Cc: max.byungchul.park@gmail.com > Cc: byungchul.park@lge.com > Signed-off-by: Joel Fernandes (Google) More comments below. Thanx, Paul > --- > kernel/rcu/rcuperf.c | 169 ++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 168 insertions(+), 1 deletion(-) > > diff --git a/kernel/rcu/rcuperf.c b/kernel/rcu/rcuperf.c > index 7a6890b23c5f..34658760da5e 100644 > --- a/kernel/rcu/rcuperf.c > +++ b/kernel/rcu/rcuperf.c > @@ -89,7 +89,7 @@ torture_param(int, writer_holdoff, 0, "Holdoff (us) between GPs, zero to disable > > static char *perf_type = "rcu"; > module_param(perf_type, charp, 0444); > -MODULE_PARM_DESC(perf_type, "Type of RCU to performance-test (rcu, rcu_bh, ...)"); > +MODULE_PARM_DESC(perf_type, "Type of RCU to performance-test (rcu, rcu_bh, kfree,...)"); > > static int nrealreaders; > static int nrealwriters; > @@ -592,6 +592,170 @@ rcu_perf_shutdown(void *arg) > return -EINVAL; > } > > +/* > + * kfree_rcu performance tests: Start a kfree_rcu loop on all CPUs for number > + * of iterations and measure total time for all iterations to complete. > + */ > + > +torture_param(int, kfree_nthreads, -1, "Number of RCU reader threads"); > +torture_param(int, kfree_alloc_num, 8000, "Number of allocations and frees done by a thread"); > +torture_param(int, kfree_alloc_size, 16, "Size of each allocation"); Is this used? How does it relate to KFREE_OBJ_BYTES? > +torture_param(int, kfree_loops, 10, "Size of each allocation"); I suspect that this kfree_loops string is out of date. > +torture_param(int, kfree_no_batch, 0, "Use the non-batching (slower) version of kfree_rcu"); All of these need to be added to kernel-parameters.txt. Along with any added by the earlier patch, for that matter. > +static struct task_struct **kfree_reader_tasks; > +static int kfree_nrealthreads; > +static atomic_t n_kfree_perf_thread_started; > +static atomic_t n_kfree_perf_thread_ended; > + > +#define KFREE_OBJ_BYTES 8 > + > +struct kfree_obj { > + char kfree_obj[KFREE_OBJ_BYTES]; > + struct rcu_head rh; > +}; > + > +void kfree_call_rcu_nobatch(struct rcu_head *head, rcu_callback_t func); > + > +static int > +kfree_perf_thread(void *arg) > +{ > + int i, l = 0; It is really easy to confuse "l" and "1" in some fonts, so please use a different name. (From the "showing my age" department: On typical 1970s typewriters, there was no numeral "1" -- you typed the letter "l" instead, thus anticipating at least the first digit of "1337".) > + long me = (long)arg; > + struct kfree_obj **alloc_ptrs; > + u64 start_time, end_time; > + > + VERBOSE_PERFOUT_STRING("kfree_perf_thread task started"); > + set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids)); > + set_user_nice(current, MAX_NICE); > + atomic_inc(&n_kfree_perf_thread_started); > + > + alloc_ptrs = (struct kfree_obj **)kmalloc(sizeof(struct kfree_obj *) * kfree_alloc_num, > + GFP_KERNEL); > + if (!alloc_ptrs) > + return -ENOMEM; > + > + start_time = ktime_get_mono_fast_ns(); Don't you want to announce that you started here rather than above in order to avoid (admittedly slight) measurement inaccuracies? > + do { > + for (i = 0; i < kfree_alloc_num; i++) { > + alloc_ptrs[i] = kmalloc(sizeof(struct kfree_obj), GFP_KERNEL); > + if (!alloc_ptrs[i]) > + return -ENOMEM; > + } > + > + for (i = 0; i < kfree_alloc_num; i++) { > + if (!kfree_no_batch) { > + kfree_rcu(alloc_ptrs[i], rh); > + } else { > + rcu_callback_t cb; > + > + cb = (rcu_callback_t)(unsigned long)offsetof(struct kfree_obj, rh); > + kfree_call_rcu_nobatch(&(alloc_ptrs[i]->rh), cb); > + } > + } > + > + schedule_timeout_uninterruptible(2); Why the two-jiffy wait in the middle of a timed test? Yes, you need a cond_resched() and maybe more here, but a two-jiffy wait? I don't see how this has any chance of getting valid measurements. What am I missing here? > + } while (!torture_must_stop() && ++l < kfree_loops); > + > + kfree(alloc_ptrs); > + > + if (atomic_inc_return(&n_kfree_perf_thread_ended) >= kfree_nrealthreads) { > + end_time = ktime_get_mono_fast_ns(); Don't we want to capture the end time before the kfree()? > + pr_alert("Total time taken by all kfree'ers: %llu ns, loops: %d\n", > + (unsigned long long)(end_time - start_time), kfree_loops); > + if (shutdown) { > + smp_mb(); /* Assign before wake. */ > + wake_up(&shutdown_wq); > + } > + } > + > + torture_kthread_stopping("kfree_perf_thread"); > + return 0; > +} > + > +static void > +kfree_perf_cleanup(void) > +{ > + int i; > + > + if (torture_cleanup_begin()) > + return; > + > + if (kfree_reader_tasks) { > + for (i = 0; i < kfree_nrealthreads; i++) > + torture_stop_kthread(kfree_perf_thread, > + kfree_reader_tasks[i]); > + kfree(kfree_reader_tasks); > + } > + > + torture_cleanup_end(); > +} > + > +/* > + * shutdown kthread. Just waits to be awakened, then shuts down system. > + */ > +static int > +kfree_perf_shutdown(void *arg) > +{ > + do { > + wait_event(shutdown_wq, > + atomic_read(&n_kfree_perf_thread_ended) >= > + kfree_nrealthreads); > + } while (atomic_read(&n_kfree_perf_thread_ended) < kfree_nrealthreads); > + > + smp_mb(); /* Wake before output. */ > + > + kfree_perf_cleanup(); > + kernel_power_off(); > + return -EINVAL; > +} Is there some way to avoid (almost) duplicating rcu_perf_shutdown()? > +static int __init > +kfree_perf_init(void) > +{ > + long i; > + int firsterr = 0; > + > + if (!torture_init_begin("kfree_perf", verbose)) > + return -EBUSY; > + > + kfree_nrealthreads = compute_real(kfree_nthreads); > + /* Start up the kthreads. */ > + if (shutdown) { > + init_waitqueue_head(&shutdown_wq); > + firsterr = torture_create_kthread(kfree_perf_shutdown, NULL, > + shutdown_task); > + if (firsterr) > + goto unwind; > + schedule_timeout_uninterruptible(1); > + } > + > + kfree_reader_tasks = kcalloc(kfree_nrealthreads, sizeof(kfree_reader_tasks[0]), > + GFP_KERNEL); > + if (kfree_reader_tasks == NULL) { > + firsterr = -ENOMEM; > + goto unwind; > + } > + > + for (i = 0; i < kfree_nrealthreads; i++) { > + firsterr = torture_create_kthread(kfree_perf_thread, (void *)i, > + kfree_reader_tasks[i]); > + if (firsterr) > + goto unwind; > + } > + > + while (atomic_read(&n_kfree_perf_thread_started) < kfree_nrealthreads) > + schedule_timeout_uninterruptible(1); > + > + torture_init_end(); > + return 0; > + > +unwind: > + torture_init_end(); > + kfree_perf_cleanup(); > + return firsterr; > +} > + > static int __init > rcu_perf_init(void) > { > @@ -601,6 +765,9 @@ rcu_perf_init(void) > &rcu_ops, &srcu_ops, &srcud_ops, &tasks_ops, > }; > > + if (strcmp(perf_type, "kfree") == 0) > + return kfree_perf_init(); > + > if (!torture_init_begin(perf_type, verbose)) > return -EBUSY; > > -- > 2.22.0.770.g0f2c4a37fd-goog >