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 Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3F1F2CDB46F for ; Tue, 23 Jun 2026 11:23:12 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wbzD8-0004NK-Bv; Tue, 23 Jun 2026 07:22:34 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wbzD7-0004N3-9C for qemu-devel@nongnu.org; Tue, 23 Jun 2026 07:22:33 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wbzD4-0002Eb-H3 for qemu-devel@nongnu.org; Tue, 23 Jun 2026 07:22:32 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1782213748; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=X0T6VopPiWt78/JJhprz1gfTKdqBVekND7Dihi7hluY=; b=ifMexwydZKIt5U0c2lXGzZ8sIbQx23PYCP2kwQXt2fSXNNlSVU4j4W5+23xVmpH0swn6mM GiPqKDa3yDkkQGnDln8k0U54S6wYIrKe7Dtb/mJR1YONhYxhynmloy208NdBhc+OUgzo+S AFaDy2HOoE1RloCCDhE3JQw1Z2vZiMA= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-616-viTeXk5dNhir2sm6p3b3JA-1; Tue, 23 Jun 2026 07:22:26 -0400 X-MC-Unique: viTeXk5dNhir2sm6p3b3JA-1 X-Mimecast-MFC-AGG-ID: viTeXk5dNhir2sm6p3b3JA_1782213745 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 25BF218001F6; Tue, 23 Jun 2026 11:22:25 +0000 (UTC) Received: from redhat.com (unknown [10.44.34.133]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9DB6E1800591; Tue, 23 Jun 2026 11:22:22 +0000 (UTC) Date: Tue, 23 Jun 2026 12:22:19 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Christian Hergert Cc: qemu-devel@nongnu.org, Hanna Reitz , qemu-block@nongnu.org, Kevin Wolf Subject: Re: [PATCH 1/1] block/vvfat: defer write commits to half-second timer Message-ID: References: <20260531103437.2896462-1-christian@sourceandstack.com> <20260531103437.2896462-2-christian@sourceandstack.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260531103437.2896462-2-christian@sourceandstack.com> User-Agent: Mutt/2.3.2 (2026-04-26) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Sun, May 31, 2026 at 12:34:37PM +0200, Christian Hergert wrote: > This keeps consistent reads but defers writes to a half-second timer by > implementing the suggested TODO in block/vvfat.c. > > I noticed slow boot performance when testing a UKI image. It was roughly > 18 seconds to a login prompt with a simple userspace. I profiled quickly > with Sysprof which showed an overwhelming amount of time spent in > check_directory_consistency(). > > The -drive in question here is the following: > > file=fat:rw:/tmp/machines-uki-esp-HVCXP3,format=raw,media=disk > > which has a temporary NvVars in it for quick throwaway VM testing which > I use in conjunction with mkosi. By NvVars are you referring to a NVRAM backing store for use with EDK2 ? If so, then newer EDK2 supports a JSON backing store which would be a better bet for quick & easy VM testing IMHO. Not an objection to this patch, but we tend to recommend that any use of vvfat is best avoided where any other alternative is available. > > With this commit in place, boot to login reduces from 18 seconds to 6. > > Signed-off-by: Christian Hergert > --- > block/vvfat.c | 130 ++++++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 125 insertions(+), 5 deletions(-) FYI, applying this patch appears to break the I/O tests for vvfat: $ ./build/run ./build/tests/qemu-iotests/check -vvfat vvfat QEMU -- "/home/berrange/src/virt/qemu/build/qemu-system-x86_64" -nodefaults -display none -accel qtest QEMU_IMG -- "/home/berrange/src/virt/qemu/build/qemu-img" QEMU_IO -- "/home/berrange/src/virt/qemu/build/qemu-io" --cache writeback --aio threads -f vvfat QEMU_NBD -- "/home/berrange/src/virt/qemu/build/qemu-nbd" IMGFMT -- vvfat IMGPROTO -- file PLATFORM -- Linux/x86_64 berrange.csb 7.0.9-205.fc44.x86_64 TEST_DIR -- /home/berrange/src/virt/qemu/scratch SOCK_DIR -- /tmp/qemu-iotests-4_wjh3ml GDB_OPTIONS -- VALGRIND_QEMU -- PRINT_QEMU_OUTPUT -- vvfat fail [12:16:35] [12:16:39] 3.3s (last: 3.2s) failed, exit status 1 --- /home/berrange/src/virt/qemu/tests/qemu-iotests/tests/vvfat.out +++ /home/berrange/src/virt/qemu/scratch/vvfat-file-vvfat/vvfat.out.bad @@ -1,5 +1,105 @@ -................ +E..F..FFFFFFF..F +====================================================================== +ERROR: test_create_file (__main__.TestVVFatDriver.test_create_file) +Test creating a new file +---------------------------------------------------------------------- +Traceback (most recent call last): + File "/home/berrange/src/virt/qemu/tests/qemu-iotests/tests/vvfat", line 477, in test_create_file + with open(os.path.join(filesystem, "newfile.txt"), "rb") as f: + ~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +FileNotFoundError: [Errno 2] No such file or directory: '/home/berrange/src/virt/qemu/scratch/vvfat-file-vvfat/filesystem/newfile.txt' + +====================================================================== +FAIL: test_modify_content_same_clusters (__main__.TestVVFatDriver.test_modify_content_same_clusters) +Test modifying the content of the file without changing the number of +---------------------------------------------------------------------- +Traceback (most recent call last): + File "/home/berrange/src/virt/qemu/tests/qemu-iotests/tests/vvfat", line 300, in test_modify_content_same_clusters + self.assertEqual(f.read(), new_content) + ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^ +AssertionError: b'Hello, world! 0\n' != b'Hello, world! Modified\n' + +====================================================================== +FAIL: test_truncate_file_change_clusters_less (__main__.TestVVFatDriver.test_truncate_file_change_clusters_less) +Test truncating a file by reducing the number of clusters +---------------------------------------------------------------------- +Traceback (most recent call last): + File "/home/berrange/src/virt/qemu/tests/qemu-iotests/tests/vvfat", line 377, in test_truncate_file_change_clusters_less + self.assertEqual(f.read(), b"A") + ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^ +AssertionError: b'AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA[16338 chars]PPPP' != b'A' + +====================================================================== +FAIL: test_truncate_file_same_clusters_less (__main__.TestVVFatDriver.test_truncate_file_same_clusters_less) +Test truncating the file without changing number of clusters +---------------------------------------------------------------------- +Traceback (most recent call last): + File "/home/berrange/src/virt/qemu/tests/qemu-iotests/tests/vvfat", line 319, in test_truncate_file_same_clusters_less + self.assertEqual(f.read(), new_content) + ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^ +AssertionError: b'Hello, world! 0\n' != b'Hello' + +====================================================================== +FAIL: test_truncate_file_same_clusters_more (__main__.TestVVFatDriver.test_truncate_file_same_clusters_more) +Test truncating the file without changing number of clusters +---------------------------------------------------------------------- +Traceback (most recent call last): + File "/home/berrange/src/virt/qemu/tests/qemu-iotests/tests/vvfat", line 343, in test_truncate_file_same_clusters_more + self.assertEqual(f.read(), new_content) + ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^ +AssertionError: b'Hello, world! 0\n' != b'Hello, world! 0\n((((' + +====================================================================== +FAIL: test_write_file_change_clusters_less (__main__.TestVVFatDriver.test_write_file_change_clusters_less) +Test truncating a file by reducing the number of clusters +---------------------------------------------------------------------- +Traceback (most recent call last): + File "/home/berrange/src/virt/qemu/tests/qemu-iotests/tests/vvfat", line 393, in test_write_file_change_clusters_less + self.assertEqual(f.read(), new_content) + ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^ +AssertionError: b'AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA[24531 chars]XXXX' != b'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX[16339 chars]YYYY' + +====================================================================== +FAIL: test_write_file_change_clusters_more (__main__.TestVVFatDriver.test_write_file_change_clusters_more) +Test truncating a file by increasing the number of clusters +---------------------------------------------------------------------- +Traceback (most recent call last): + File "/home/berrange/src/virt/qemu/tests/qemu-iotests/tests/vvfat", line 415, in test_write_file_change_clusters_more + self.assertEqual(f.read(), new_content) + ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^ +AssertionError: b'AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA[24531 chars]XXXX' != b'WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW[32723 chars]ZZZZ' + +====================================================================== +FAIL: test_write_file_change_clusters_more_non_contiguous_2_mappings (__main__.TestVVFatDriver.test_write_file_change_clusters_more_non_contiguous_2_mappings) +Test truncating a file by increasing the number of clusters Here we +---------------------------------------------------------------------- +Traceback (most recent call last): + File "/home/berrange/src/virt/qemu/tests/qemu-iotests/tests/vvfat", line 435, in test_write_file_change_clusters_more_non_contiguous_2_mappings + self.assertEqual(f.read(), new_content) + ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^ +AssertionError: b'AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA[16339 chars]PPPP' != b'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX[24531 chars]ZZZZ' + +====================================================================== +FAIL: test_write_file_change_clusters_more_non_contiguous_3_mappings (__main__.TestVVFatDriver.test_write_file_change_clusters_more_non_contiguous_3_mappings) +Test truncating a file by increasing the number of clusters Here we +---------------------------------------------------------------------- +Traceback (most recent call last): + File "/home/berrange/src/virt/qemu/tests/qemu-iotests/tests/vvfat", line 460, in test_write_file_change_clusters_more_non_contiguous_3_mappings + self.assertEqual(f.read(), new_content) + ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^ +AssertionError: b'AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA[16339 chars]PPPP' != b'WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW[32723 chars]ZZZZ' + +====================================================================== +FAIL: test_write_large_file (__main__.TestVVFatDriver.test_write_large_file) +Test writing a large file +---------------------------------------------------------------------- +Traceback (most recent call last): + File "/home/berrange/src/virt/qemu/tests/qemu-iotests/tests/vvfat", line 362, in test_write_large_file + self.assertEqual(f.read(), new_content) + ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^ +AssertionError: b'AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA[16339 chars]PPPP' != b'ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ[16339 chars]KKKK' + ---------------------------------------------------------------------- Ran 16 tests -OK +FAILED (failures=9, errors=1) Failures: vvfat Failed 1 of 1 iotests I didn't investigate whether this is a real functional bug, or whether the tests are making bad assumptions that need fixing, or whether this is just inherant behaviour from delaying writes. > > diff --git a/block/vvfat.c b/block/vvfat.c > index e334b9febb..49756ac5e0 100644 > --- a/block/vvfat.c > +++ b/block/vvfat.c > @@ -32,6 +32,7 @@ > #include "block/qdict.h" > #include "qemu/module.h" > #include "qemu/option.h" > +#include "qemu/timer.h" > #include "qemu/bswap.h" > #include "migration/blocker.h" > #include "qobject/qdict.h" > @@ -53,8 +54,6 @@ > Note that DOS assumes the system files to be the first files in the > file system (test if the boot sector still relies on that fact)! */ > /* MAYBE TODO: write block-visofs.c */ > -/* TODO: call try_commit() only after a timeout */ > - > /* #define DEBUG */ > > #ifdef DEBUG > @@ -80,6 +79,8 @@ static void checkpoint(void); > #define DIR_KANJI_FAKE 0x05 > #define DIR_FREE 0x00 > > +#define VVFAT_COMMIT_DELAY_NS (NANOSECONDS_PER_SECOND / 2) > + > /* dynamic array functions */ > typedef struct array_t { > char* pointer; > @@ -332,6 +333,8 @@ typedef struct BDRVVVFATState { > void* fat2; > char* used_clusters; > array_t commits; > + QEMUTimer *commit_timer; > + bool commit_pending; > const char* path; > int downcase_short_names; > > @@ -1052,6 +1055,8 @@ static BDRVVVFATState *vvv = NULL; > > static int enable_write_target(BlockDriverState *bs, Error **errp); > static int coroutine_fn is_consistent(BDRVVVFATState *s); > +static void vvfat_attach_aio_context(BlockDriverState *bs, > + AioContext *new_context); > > static QemuOptsList runtime_opts = { > .name = "vvfat", > @@ -1278,6 +1283,7 @@ static int vvfat_open(BlockDriverState *bs, QDict *options, int flags, > } > > qemu_co_mutex_init(&s->lock); > + vvfat_attach_aio_context(bs, bdrv_get_aio_context(bs)); > > qemu_opts_del(opts); > > @@ -2973,6 +2979,60 @@ DLOG(checkpoint()); > return do_commit(s); > } > > +static int coroutine_fn GRAPH_RDLOCK > +vvfat_commit_now(BDRVVVFATState *s) > +{ > + int ret; > + > + if (s->commit_timer) { > + timer_del(s->commit_timer); > + } > + if (!s->commit_pending) { > + return 0; > + } > + > + qemu_co_mutex_lock(&s->lock); > + ret = try_commit(s); > + qemu_co_mutex_unlock(&s->lock); > + > + if (ret == 0) { > + s->commit_pending = false; > + } > + > + return ret; > +} > + > +static void coroutine_fn vvfat_commit_timer_entry(void *opaque) > +{ > + BlockDriverState *bs = opaque; > + BDRVVVFATState *s = bs->opaque; > + GRAPH_RDLOCK_GUARD(); > + > + vvfat_commit_now(s); > + bdrv_dec_in_flight(bs); > +} > + > +static void vvfat_commit_timer_cb(void *opaque) > +{ > + BlockDriverState *bs = opaque; > + Coroutine *co; > + > + co = qemu_coroutine_create(vvfat_commit_timer_entry, bs); > + bdrv_inc_in_flight(bs); > + qemu_coroutine_enter(co); > +} > + > +static void vvfat_schedule_commit(BDRVVVFATState *s) > +{ > + s->commit_pending = true; > + > + if (s->commit_timer) { > + timer_mod_ns(s->commit_timer, > + qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + > + VVFAT_COMMIT_DELAY_NS); > + } > +} > + > static int coroutine_fn GRAPH_RDLOCK > vvfat_write(BlockDriverState *bs, int64_t sector_num, > const uint8_t *buf, int nb_sectors) > @@ -3098,8 +3158,7 @@ DLOG(fprintf(stderr, "Write to qcow backend: %d + %d\n", (int)sector_num, nb_sec > } > > DLOG(checkpoint()); > - /* TODO: add timeout */ > - try_commit(s); > + vvfat_schedule_commit(s); > > DLOG(checkpoint()); > return 0; > @@ -3133,6 +3192,34 @@ vvfat_co_pwritev(BlockDriverState *bs, int64_t offset, int64_t bytes, > return ret; > } > > +static int coroutine_fn GRAPH_RDLOCK > +vvfat_co_flush(BlockDriverState *bs) > +{ > + BDRVVVFATState *s = bs->opaque; > + > + if (s->qcow == NULL) { > + return 0; > + } > + > + return vvfat_commit_now(s); > +} > + > +static void vvfat_drain_begin(BlockDriverState *bs) > +{ > + BDRVVVFATState *s = bs->opaque; > + Coroutine *co; > + > + if (!s->commit_timer || !timer_pending(s->commit_timer)) { > + return; > + } > + > + timer_del(s->commit_timer); > + > + co = qemu_coroutine_create(vvfat_commit_timer_entry, bs); > + bdrv_inc_in_flight(bs); > + aio_co_enter(bdrv_get_aio_context(bs), co); > +} > + > static int coroutine_fn vvfat_co_block_status(BlockDriverState *bs, > unsigned int mode, > int64_t offset, int64_t bytes, > @@ -3229,6 +3316,11 @@ static void vvfat_close(BlockDriverState *bs) > { > BDRVVVFATState *s = bs->opaque; > > + if (s->commit_timer) { > + timer_free(s->commit_timer); > + s->commit_timer = NULL; > + } > + > vvfat_close_current_file(s); > array_free(&(s->fat)); > array_free(&(s->directory)); > @@ -3240,6 +3332,30 @@ static void vvfat_close(BlockDriverState *bs) > } > } > > +static void vvfat_detach_aio_context(BlockDriverState *bs) > +{ > + BDRVVVFATState *s = bs->opaque; > + > + if (s->commit_timer) { > + timer_free(s->commit_timer); > + s->commit_timer = NULL; > + } > +} > + > +static void vvfat_attach_aio_context(BlockDriverState *bs, > + AioContext *new_context) > +{ > + BDRVVVFATState *s = bs->opaque; > + > + if (s->qcow) { > + s->commit_timer = aio_timer_new(new_context, QEMU_CLOCK_VIRTUAL, > + SCALE_NS, vvfat_commit_timer_cb, bs); > + if (s->commit_pending) { > + vvfat_schedule_commit(s); > + } > + } > +} > + > static const char *const vvfat_strong_runtime_opts[] = { > "dir", > "fat-type", > @@ -3263,7 +3379,11 @@ static BlockDriver bdrv_vvfat = { > > .bdrv_co_preadv = vvfat_co_preadv, > .bdrv_co_pwritev = vvfat_co_pwritev, > - .bdrv_co_block_status = vvfat_co_block_status, > + .bdrv_co_flush = vvfat_co_flush, > + .bdrv_drain_begin = vvfat_drain_begin, > + .bdrv_co_block_status = vvfat_co_block_status, > + .bdrv_detach_aio_context = vvfat_detach_aio_context, > + .bdrv_attach_aio_context = vvfat_attach_aio_context, > > .strong_runtime_opts = vvfat_strong_runtime_opts, > }; > -- > 2.54.0 > > With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|