From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ADCADC433E0 for ; Thu, 11 Mar 2021 01:15:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7303464E77 for ; Thu, 11 Mar 2021 01:15:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229459AbhCKBPL (ORCPT ); Wed, 10 Mar 2021 20:15:11 -0500 Received: from mail.kernel.org ([198.145.29.99]:58224 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229520AbhCKBPH (ORCPT ); Wed, 10 Mar 2021 20:15:07 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id D763564E77; Thu, 11 Mar 2021 01:15:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1615425307; bh=jAa/pi5t3DFRYAGhnd36XTy1+ZkK4exkr8vail6wR/8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VEwSTrBN0VKy5oUi6i7mlGz3rrIbJJATyskoPLObXi9HOhEiIGBeceV1n9aji6KB1 73BhwXiLT7zwVnTTxiM3Wz/O5Ubm0eRvIrAptF+CETTqbZOOT/dtvjcyfITLxWoF/Q 7AJYF7U9rvCrACNj10ZzK8u3G8PrGCb/ZQWuRbJVlEFoES5sLl+RSx1R/bt0kc/2jl l4cYCxAQqc/hf9N2dpbz/L7O2kGpAK5MrLa48edODKEk2yqnrQjbCylvw7SF8ejFl1 D4SNWTdIh8pjavNDS2bL7rg/x++kd39SjEwpXnCQNjNwpx4HyzxkVov5bFVQ3Fwop6 uwWAxUY0PU0gg== Date: Wed, 10 Mar 2021 17:15:05 -0800 From: "Darrick J. Wong" To: Dave Chinner Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH 40/45] xfs: convert CIL to unordered per cpu lists Message-ID: <20210311011505.GN3419940@magnolia> References: <20210305051143.182133-1-david@fromorbit.com> <20210305051143.182133-41-david@fromorbit.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210305051143.182133-41-david@fromorbit.com> Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Fri, Mar 05, 2021 at 04:11:38PM +1100, Dave Chinner wrote: > From: Dave Chinner > > So that we can remove the cil_lock which is a global serialisation > point. We've already got ordering sorted, so all we need to do is > treat the CIL list like the busy extent list and reconstruct it > before the push starts. > > This is what we're trying to avoid: > > - 75.35% 1.83% [kernel] [k] xfs_log_commit_cil > - 46.35% xfs_log_commit_cil > - 41.54% _raw_spin_lock > - 67.30% do_raw_spin_lock > 66.96% __pv_queued_spin_lock_slowpath > > Which happens on a 32p system when running a 32-way 'rm -rf' > workload. After this patch: > > - 20.90% 3.23% [kernel] [k] xfs_log_commit_cil > - 17.67% xfs_log_commit_cil > - 6.51% xfs_log_ticket_ungrant > 1.40% xfs_log_space_wake > 2.32% memcpy_erms > - 2.18% xfs_buf_item_committing > - 2.12% xfs_buf_item_release > - 1.03% xfs_buf_unlock > 0.96% up > 0.72% xfs_buf_rele > 1.33% xfs_inode_item_format > 1.19% down_read > 0.91% up_read > 0.76% xfs_buf_item_format > - 0.68% kmem_alloc_large > - 0.67% kmem_alloc > 0.64% __kmalloc > 0.50% xfs_buf_item_size > > It kinda looks like the workload is running out of log space all > the time. But all the spinlock contention is gone and the > transaction commit rate has gone from 800k/s to 1.3M/s so the amount > of real work being done has gone up a *lot*. > > Signed-off-by: Dave Chinner > --- > fs/xfs/xfs_log_cil.c | 61 ++++++++++++++++++++----------------------- > fs/xfs/xfs_log_priv.h | 2 -- > 2 files changed, 29 insertions(+), 34 deletions(-) > > diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c > index 7420389f4cee..3d43a5088154 100644 > --- a/fs/xfs/xfs_log_cil.c > +++ b/fs/xfs/xfs_log_cil.c > @@ -448,10 +448,9 @@ xlog_cil_insert_items( > /* > * We need to take the CIL checkpoint unit reservation on the first > * commit into the CIL. Test the XLOG_CIL_EMPTY bit first so we don't > - * unnecessarily do an atomic op in the fast path here. We don't need to > - * hold the xc_cil_lock here to clear the XLOG_CIL_EMPTY bit as we are > - * under the xc_ctx_lock here and that needs to be held exclusively to > - * reset the XLOG_CIL_EMPTY bit. > + * unnecessarily do an atomic op in the fast path here. We can clear the > + * XLOG_CIL_EMPTY bit as we are under the xc_ctx_lock here and that > + * needs to be held exclusively to reset the XLOG_CIL_EMPTY bit. > */ > if (test_bit(XLOG_CIL_EMPTY, &cil->xc_flags) && > test_and_clear_bit(XLOG_CIL_EMPTY, &cil->xc_flags)) > @@ -505,24 +504,6 @@ xlog_cil_insert_items( > /* attach the transaction to the CIL if it has any busy extents */ > if (!list_empty(&tp->t_busy)) > list_splice_init(&tp->t_busy, &cilpcp->busy_extents); > - put_cpu_ptr(cilpcp); > - > - /* > - * If we've overrun the reservation, dump the tx details before we move > - * the log items. Shutdown is imminent... > - */ > - tp->t_ticket->t_curr_res -= ctx_res + len; > - if (WARN_ON(tp->t_ticket->t_curr_res < 0)) { > - xfs_warn(log->l_mp, "Transaction log reservation overrun:"); > - xfs_warn(log->l_mp, > - " log items: %d bytes (iov hdrs: %d bytes)", > - len, iovhdr_res); > - xfs_warn(log->l_mp, " split region headers: %d bytes", > - split_res); > - xfs_warn(log->l_mp, " ctx ticket: %d bytes", ctx_res); > - xlog_print_trans(tp); > - } > - > /* > * Now update the order of everything modified in the transaction > * and insert items into the CIL if they aren't already there. > @@ -530,7 +511,6 @@ xlog_cil_insert_items( > * the transaction commit. > */ > order = atomic_inc_return(&ctx->order_id); > - spin_lock(&cil->xc_cil_lock); > list_for_each_entry(lip, &tp->t_items, li_trans) { > > /* Skip items which aren't dirty in this transaction. */ > @@ -540,10 +520,26 @@ xlog_cil_insert_items( > lip->li_order_id = order; > if (!list_empty(&lip->li_cil)) > continue; > - list_add(&lip->li_cil, &cil->xc_cil); > + list_add(&lip->li_cil, &cilpcp->log_items); Ok, so if I understand this correctly -- every time a transaction commits, it marks every dirty log item with a monotonically increasing counter. If the log item isn't already on another CPU's CIL list, it gets added to the current CPU's CIL list... > + } > + put_cpu_ptr(cilpcp); > + > + /* > + * If we've overrun the reservation, dump the tx details before we move > + * the log items. Shutdown is imminent... > + */ > + tp->t_ticket->t_curr_res -= ctx_res + len; > + if (WARN_ON(tp->t_ticket->t_curr_res < 0)) { > + xfs_warn(log->l_mp, "Transaction log reservation overrun:"); > + xfs_warn(log->l_mp, > + " log items: %d bytes (iov hdrs: %d bytes)", > + len, iovhdr_res); > + xfs_warn(log->l_mp, " split region headers: %d bytes", > + split_res); > + xfs_warn(log->l_mp, " ctx ticket: %d bytes", ctx_res); > + xlog_print_trans(tp); > } > > - spin_unlock(&cil->xc_cil_lock); > > if (tp->t_ticket->t_curr_res < 0) > xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR); > @@ -806,6 +802,7 @@ xlog_cil_push_work( > bool commit_iclog_sync = false; > int cpu; > struct xlog_cil_pcp *cilpcp; > + LIST_HEAD (log_items); > > new_ctx = xlog_cil_ctx_alloc(); > new_ctx->ticket = xlog_cil_ticket_alloc(log); > @@ -822,6 +819,9 @@ xlog_cil_push_work( > list_splice_init(&cilpcp->busy_extents, > &ctx->busy_extents); > } > + if (!list_empty(&cilpcp->log_items)) { > + list_splice_init(&cilpcp->log_items, &log_items); ...and then at CIL push time, we splice each per-CPU list into a big list, sort the dirty log items by counter number, and process them. The first thought I had was that it's a darn shame that _insert_items can't steal a log item from another CPU's CIL list, because you could then mergesort the per-CPU CIL lists into @log_items. Unfortunately, I don't think there's a safe way to steal items from a per-CPU list without involving locks. The second thought I had was that we have the xfs_pwork mechanism for launching a bunch of worker threads. A pwork workqueue is (probably) too costly when the item list is short or there aren't that many CPUs, but once list_sort starts getting painful, would it be faster to launch a bunch of threads in push_work to sort each per-CPU list and then merge sort them into the final list? FWIW at least mechanically, the last two patches look reasonable to me. --D > + } > } > > spin_lock(&cil->xc_push_lock); > @@ -907,12 +907,12 @@ xlog_cil_push_work( > * needed on the transaction commit side which is currently locked out > * by the flush lock. > */ > - list_sort(NULL, &cil->xc_cil, xlog_cil_order_cmp); > + list_sort(NULL, &log_items, xlog_cil_order_cmp); > lv = NULL; > - while (!list_empty(&cil->xc_cil)) { > + while (!list_empty(&log_items)) { > struct xfs_log_item *item; > > - item = list_first_entry(&cil->xc_cil, > + item = list_first_entry(&log_items, > struct xfs_log_item, li_cil); > list_del_init(&item->li_cil); > item->li_order_id = 0; > @@ -1099,7 +1099,6 @@ xlog_cil_push_background( > * The cil won't be empty because we are called while holding the > * context lock so whatever we added to the CIL will still be there. > */ > - ASSERT(!list_empty(&cil->xc_cil)); > ASSERT(!test_bit(XLOG_CIL_EMPTY, &cil->xc_flags)); > > /* > @@ -1491,6 +1490,7 @@ xlog_cil_pcp_alloc( > for_each_possible_cpu(cpu) { > cilpcp = per_cpu_ptr(pcptr, cpu); > INIT_LIST_HEAD(&cilpcp->busy_extents); > + INIT_LIST_HEAD(&cilpcp->log_items); > } > > if (xlog_cil_pcp_hpadd(cil) < 0) { > @@ -1531,9 +1531,7 @@ xlog_cil_init( > return -ENOMEM; > } > > - INIT_LIST_HEAD(&cil->xc_cil); > INIT_LIST_HEAD(&cil->xc_committing); > - spin_lock_init(&cil->xc_cil_lock); > spin_lock_init(&cil->xc_push_lock); > init_waitqueue_head(&cil->xc_push_wait); > init_rwsem(&cil->xc_ctx_lock); > @@ -1559,7 +1557,6 @@ xlog_cil_destroy( > kmem_free(cil->xc_ctx); > } > > - ASSERT(list_empty(&cil->xc_cil)); > ASSERT(test_bit(XLOG_CIL_EMPTY, &cil->xc_flags)); > xlog_cil_pcp_free(cil, cil->xc_pcp); > kmem_free(cil); > diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h > index 92d9e1a03a07..12a1a36eef7e 100644 > --- a/fs/xfs/xfs_log_priv.h > +++ b/fs/xfs/xfs_log_priv.h > @@ -262,8 +262,6 @@ struct xfs_cil { > struct xlog *xc_log; > unsigned long xc_flags; > atomic_t xc_iclog_hdrs; > - struct list_head xc_cil; > - spinlock_t xc_cil_lock; > > struct rw_semaphore xc_ctx_lock ____cacheline_aligned_in_smp; > struct xfs_cil_ctx *xc_ctx; > -- > 2.28.0 >