From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
To: Emanuele Giuseppe Esposito <eesposit@redhat.com>, qemu-block@nongnu.org
Cc: John Snow <jsnow@redhat.com>, Kevin Wolf <kwolf@redhat.com>,
Max Reitz <mreitz@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
qemu-devel@nongnu.org
Subject: Re: [PATCH v2 1/7] block-copy: streamline choice of copy_range vs. read/write
Date: Thu, 20 May 2021 17:42:35 +0300 [thread overview]
Message-ID: <f5069a9d-cd23-26cf-c1cb-6f4f5774e48d@virtuozzo.com> (raw)
In-Reply-To: <20210518100757.31243-2-eesposit@redhat.com>
18.05.2021 13:07, Emanuele Giuseppe Esposito wrote:
> From: Paolo Bonzini <pbonzini@redhat.com>
>
> Put the logic to determine the copy size in a separate function, so
> that there is a simple state machine for the possible methods of
> copying data from one BlockDriverState to the other.
Honestly, for me 4-state state-maching + function to determine copy-size doesn't seem better than two simple variables copy_size and use_copy_range.
What's the benefit of it?
>
> While at it, store the common computation of block_copy_max_transfer
> into a new field of BlockCopyState, and make sure that we always
> obey max_transfer; that's more efficient even for the
> COPY_RANGE_READ_WRITE case.
hmm, maybe. It could be a separate patch.
>
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> block/block-copy.c | 59 ++++++++++++++++++++++++++++++----------------
stats agree with me, that its' not a simplification.
> 1 file changed, 39 insertions(+), 20 deletions(-)
>
> diff --git a/block/block-copy.c b/block/block-copy.c
> index 37c8e8504b..10ce51a244 100644
> --- a/block/block-copy.c
> +++ b/block/block-copy.c
> @@ -28,6 +28,13 @@
> #define BLOCK_COPY_MAX_WORKERS 64
> #define BLOCK_COPY_SLICE_TIME 100000000ULL /* ns */
>
> +typedef enum {
> + COPY_READ_WRITE_CLUSTER,
> + COPY_READ_WRITE,
> + COPY_RANGE_SMALL,
> + COPY_RANGE_FULL
> +} BlockCopyMethod;
> +
> static coroutine_fn int block_copy_task_entry(AioTask *task);
>
> typedef struct BlockCopyCallState {
> @@ -85,8 +92,8 @@ typedef struct BlockCopyState {
> BdrvDirtyBitmap *copy_bitmap;
> int64_t in_flight_bytes;
> int64_t cluster_size;
> - bool use_copy_range;
> - int64_t copy_size;
> + BlockCopyMethod method;
> + int64_t max_transfer;
> uint64_t len;
> QLIST_HEAD(, BlockCopyTask) tasks; /* All tasks from all block-copy calls */
> QLIST_HEAD(, BlockCopyCallState) calls;
> @@ -148,6 +155,23 @@ static bool coroutine_fn block_copy_wait_one(BlockCopyState *s, int64_t offset,
> return true;
> }
>
> +static inline int64_t block_copy_chunk_size(BlockCopyState *s)
"inline" word does nothing in static definitions in c files. Compiler make a decision independently of it.
> +{
> + switch (s->method) {
> + case COPY_READ_WRITE_CLUSTER:
> + return s->cluster_size;
> + case COPY_READ_WRITE:
> + case COPY_RANGE_SMALL:
> + return MIN(MAX(s->cluster_size, BLOCK_COPY_MAX_BUFFER),
> + s->max_transfer);
> + case COPY_RANGE_FULL:
> + return MIN(MAX(s->cluster_size, BLOCK_COPY_MAX_COPY_RANGE),
> + s->max_transfer);
> + default:
> + abort();
> + }
> +}
> +
> /*
> * Search for the first dirty area in offset/bytes range and create task at
> * the beginning of it.
> @@ -157,8 +181,9 @@ static BlockCopyTask *block_copy_task_create(BlockCopyState *s,
> int64_t offset, int64_t bytes)
> {
> BlockCopyTask *task;
> - int64_t max_chunk = MIN_NON_ZERO(s->copy_size, call_state->max_chunk);
> + int64_t max_chunk = block_copy_chunk_size(s);
>
> + max_chunk = MIN_NON_ZERO(max_chunk, call_state->max_chunk);
> if (!bdrv_dirty_bitmap_next_dirty_area(s->copy_bitmap,
> offset, offset + bytes,
> max_chunk, &offset, &bytes))
> @@ -265,28 +290,27 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
> .len = bdrv_dirty_bitmap_size(copy_bitmap),
> .write_flags = write_flags,
> .mem = shres_create(BLOCK_COPY_MAX_MEM),
> + .max_transfer = QEMU_ALIGN_DOWN(block_copy_max_transfer(source, target)
> + , cluster_size),
> };
>
> - if (block_copy_max_transfer(source, target) < cluster_size) {
> + if (s->max_transfer < cluster_size) {
> /*
> * copy_range does not respect max_transfer. We don't want to bother
> * with requests smaller than block-copy cluster size, so fallback to
> * buffered copying (read and write respect max_transfer on their
> * behalf).
> */
> - s->use_copy_range = false;
> - s->copy_size = cluster_size;
> + s->method = COPY_READ_WRITE_CLUSTER;
> } else if (write_flags & BDRV_REQ_WRITE_COMPRESSED) {
> /* Compression supports only cluster-size writes and no copy-range. */
> - s->use_copy_range = false;
> - s->copy_size = cluster_size;
> + s->method = COPY_READ_WRITE_CLUSTER;
> } else {
> /*
> * We enable copy-range, but keep small copy_size, until first
> * successful copy_range (look at block_copy_do_copy).
> */
> - s->use_copy_range = use_copy_range;
> - s->copy_size = MAX(s->cluster_size, BLOCK_COPY_MAX_BUFFER);
> + s->method = use_copy_range ? COPY_RANGE_SMALL : COPY_READ_WRITE;
> }
>
> ratelimit_init(&s->rate_limit);
> @@ -369,30 +393,25 @@ static int coroutine_fn block_copy_do_copy(BlockCopyState *s,
> return ret;
> }
>
> - if (s->use_copy_range) {
> + if (s->method >= COPY_RANGE_SMALL) {
I don't like such condition:
1. it forces me to go to enum definition to understand the logic
2. it's error prone: it's very possibly to forget to update it, when updating the enum, and logic will be broken.
No, I don't like moving to state machine for this simple thing.
> ret = bdrv_co_copy_range(s->source, offset, s->target, offset, nbytes,
> 0, s->write_flags);
> if (ret < 0) {
> trace_block_copy_copy_range_fail(s, offset, ret);
> - s->use_copy_range = false;
> - s->copy_size = MAX(s->cluster_size, BLOCK_COPY_MAX_BUFFER);
> + s->method = COPY_READ_WRITE;
> /* Fallback to read+write with allocated buffer */
> } else {
> - if (s->use_copy_range) {
> + if (s->method == COPY_RANGE_SMALL) {
> /*
> * Successful copy-range. Now increase copy_size. copy_range
> * does not respect max_transfer (it's a TODO), so we factor
> * that in here.
> *
> - * Note: we double-check s->use_copy_range for the case when
> + * Note: we double-check s->method for the case when
> * parallel block-copy request unsets it during previous
> * bdrv_co_copy_range call.
> */
> - s->copy_size =
> - MIN(MAX(s->cluster_size, BLOCK_COPY_MAX_COPY_RANGE),
> - QEMU_ALIGN_DOWN(block_copy_max_transfer(s->source,
> - s->target),
> - s->cluster_size));
> + s->method = COPY_RANGE_FULL;
> }
> goto out;
> }
>
--
Best regards,
Vladimir
next prev parent reply other threads:[~2021-05-20 14:52 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-18 10:07 [PATCH v2 0/7] block-copy: protect block-copy internal structures Emanuele Giuseppe Esposito
2021-05-18 10:07 ` [PATCH v2 1/7] block-copy: streamline choice of copy_range vs. read/write Emanuele Giuseppe Esposito
2021-05-20 14:42 ` Vladimir Sementsov-Ogievskiy [this message]
2021-05-20 15:06 ` Emanuele Giuseppe Esposito
2021-05-20 15:24 ` Vladimir Sementsov-Ogievskiy
2021-05-21 15:10 ` Paolo Bonzini
2021-05-21 15:48 ` Vladimir Sementsov-Ogievskiy
2021-05-21 16:43 ` Paolo Bonzini
2021-05-21 17:51 ` Vladimir Sementsov-Ogievskiy
2021-05-27 8:20 ` Stefan Hajnoczi
2021-05-27 19:04 ` Paolo Bonzini
2021-05-18 10:07 ` [PATCH v2 2/7] block-copy: improve documentation of BlockCopyTask and BlockCopyState types and functions Emanuele Giuseppe Esposito
2021-05-20 15:00 ` Vladimir Sementsov-Ogievskiy
2021-05-20 15:15 ` Emanuele Giuseppe Esposito
2021-05-18 10:07 ` [PATCH v2 3/7] block-copy: move progress_set_remaining in block_copy_task_end Emanuele Giuseppe Esposito
2021-05-20 15:03 ` Vladimir Sementsov-Ogievskiy
2021-05-18 10:07 ` [PATCH v2 4/7] block-copy: add a CoMutex to the BlockCopyTask list Emanuele Giuseppe Esposito
2021-05-20 15:19 ` Vladimir Sementsov-Ogievskiy
2021-05-25 10:07 ` Emanuele Giuseppe Esposito
2021-05-25 10:25 ` Vladimir Sementsov-Ogievskiy
2021-05-26 14:58 ` Paolo Bonzini
2021-05-26 16:13 ` Vladimir Sementsov-Ogievskiy
2021-05-27 9:07 ` Stefan Hajnoczi
2021-05-18 10:07 ` [PATCH v2 5/7] block-copy: add QemuMutex lock for BlockCopyCallState list Emanuele Giuseppe Esposito
2021-05-20 15:30 ` Vladimir Sementsov-Ogievskiy
2021-05-21 15:01 ` Paolo Bonzini
2021-05-25 10:58 ` Emanuele Giuseppe Esposito
2021-05-26 14:49 ` Paolo Bonzini
2021-05-28 10:53 ` Paolo Bonzini
2021-05-18 10:07 ` [PATCH v2 6/7] block-copy: atomic .cancelled and .finished fields in BlockCopyCallState Emanuele Giuseppe Esposito
2021-05-20 15:34 ` Vladimir Sementsov-Ogievskiy
2021-05-21 15:02 ` Paolo Bonzini
2021-05-21 15:53 ` Vladimir Sementsov-Ogievskiy
2021-05-21 15:56 ` Vladimir Sementsov-Ogievskiy
2021-05-21 16:47 ` Paolo Bonzini
2021-05-18 10:07 ` [PATCH v2 7/7] block-copy: protect BlockCopyState .method fields Emanuele Giuseppe Esposito
2021-05-21 17:10 ` Vladimir Sementsov-Ogievskiy
2021-05-25 10:18 ` Emanuele Giuseppe Esposito
2021-05-25 11:00 ` Vladimir Sementsov-Ogievskiy
2021-05-26 14:48 ` Paolo Bonzini
2021-05-26 17:18 ` Vladimir Sementsov-Ogievskiy
2021-05-28 10:24 ` Paolo Bonzini
2021-05-28 11:01 ` Paolo Bonzini
2021-05-28 11:52 ` Vladimir Sementsov-Ogievskiy
2021-05-28 12:44 ` Vladimir Sementsov-Ogievskiy
2021-05-20 13:47 ` [PATCH v2 0/7] block-copy: protect block-copy internal structures Vladimir Sementsov-Ogievskiy
2021-05-20 14:33 ` Emanuele Giuseppe Esposito
2021-05-27 10:31 ` Stefan Hajnoczi
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