From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35493) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z4oPs-0005wx-UX for qemu-devel@nongnu.org; Tue, 16 Jun 2015 06:48:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z4oPq-0002R8-1s for qemu-devel@nongnu.org; Tue, 16 Jun 2015 06:48:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41597) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z4oPp-0002R2-PD for qemu-devel@nongnu.org; Tue, 16 Jun 2015 06:48:26 -0400 Date: Tue, 16 Jun 2015 11:48:20 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20150616104819.GA2119@work-vm> References: <1424883128-9841-1-git-send-email-dgilbert@redhat.com> <1424883128-9841-35-git-send-email-dgilbert@redhat.com> <20150324021524.GY25043@voom.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150324021524.GY25043@voom.fritz.box> Subject: Re: [Qemu-devel] [PATCH v5 34/45] Page request: Consume pages off the post-copy queue List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: aarcange@redhat.com, yamahata@private.email.ne.jp, quintela@redhat.com, qemu-devel@nongnu.org, amit.shah@redhat.com, pbonzini@redhat.com * David Gibson (david@gibson.dropbear.id.au) wrote: > On Wed, Feb 25, 2015 at 04:51:57PM +0000, Dr. David Alan Gilbert (git) wrote: > > From: "Dr. David Alan Gilbert" > > > > When transmitting RAM pages, consume pages that have been queued by > > MIG_RPCOMM_REQPAGE commands and send them ahead of normal page scanning. > > > > Note: > > a) After a queued page the linear walk carries on from after the > > unqueued page; there is a reasonable chance that the destination > > was about to ask for other closeby pages anyway. > > > > b) We have to be careful of any assumptions that the page walking > > code makes, in particular it does some short cuts on its first linear > > walk that break as soon as we do a queued page. > > > > Signed-off-by: Dr. David Alan Gilbert > > --- > > arch_init.c | 154 +++++++++++++++++++++++++++++++++++++++++++++++++---------- > > trace-events | 2 + > > 2 files changed, 131 insertions(+), 25 deletions(-) > > > > diff --git a/arch_init.c b/arch_init.c > > index 9d8fc6b..acf65e1 100644 > > --- a/arch_init.c > > +++ b/arch_init.c > > @@ -328,6 +328,7 @@ static RAMBlock *last_seen_block; > > /* This is the last block from where we have sent data */ > > static RAMBlock *last_sent_block; > > static ram_addr_t last_offset; > > +static bool last_was_from_queue; > > static unsigned long *migration_bitmap; > > static uint64_t migration_dirty_pages; > > static uint32_t last_version; > > @@ -461,6 +462,19 @@ static inline bool migration_bitmap_set_dirty(ram_addr_t addr) > > return ret; > > } > > > > +static inline bool migration_bitmap_clear_dirty(ram_addr_t addr) > > +{ > > + bool ret; > > + int nr = addr >> TARGET_PAGE_BITS; > > + > > + ret = test_and_clear_bit(nr, migration_bitmap); > > + > > + if (ret) { > > + migration_dirty_pages--; > > + } > > + return ret; > > +} > > + > > static void migration_bitmap_sync_range(ram_addr_t start, ram_addr_t length) > > { > > ram_addr_t addr; > > @@ -669,6 +683,39 @@ static int ram_save_page(QEMUFile *f, RAMBlock* block, ram_addr_t offset, > > } > > > > /* > > + * Unqueue a page from the queue fed by postcopy page requests > > + * > > + * Returns: The RAMBlock* to transmit from (or NULL if the queue is empty) > > + * ms: MigrationState in > > + * offset: the byte offset within the RAMBlock for the start of the page > > + * ram_addr_abs: global offset in the dirty/sent bitmaps > > + */ > > +static RAMBlock *ram_save_unqueue_page(MigrationState *ms, ram_addr_t *offset, > > + ram_addr_t *ram_addr_abs) > > +{ > > + RAMBlock *result = NULL; > > + qemu_mutex_lock(&ms->src_page_req_mutex); > > + if (!QSIMPLEQ_EMPTY(&ms->src_page_requests)) { > > + struct MigrationSrcPageRequest *entry = > > + QSIMPLEQ_FIRST(&ms->src_page_requests); > > + result = entry->rb; > > + *offset = entry->offset; > > + *ram_addr_abs = (entry->offset + entry->rb->offset) & TARGET_PAGE_MASK; > > + > > + if (entry->len > TARGET_PAGE_SIZE) { > > + entry->len -= TARGET_PAGE_SIZE; > > + entry->offset += TARGET_PAGE_SIZE; > > + } else { > > + QSIMPLEQ_REMOVE_HEAD(&ms->src_page_requests, next_req); > > + g_free(entry); > > + } > > + } > > + qemu_mutex_unlock(&ms->src_page_req_mutex); > > + > > + return result; > > +} > > + > > +/* > > * Queue the pages for transmission, e.g. a request from postcopy destination > > * ms: MigrationStatus in which the queue is held > > * rbname: The RAMBlock the request is for - may be NULL (to mean reuse last) > > @@ -732,46 +779,102 @@ int ram_save_queue_pages(MigrationState *ms, const char *rbname, > > > > static int ram_find_and_save_block(QEMUFile *f, bool last_stage) > > { > > + MigrationState *ms = migrate_get_current(); > > RAMBlock *block = last_seen_block; > > + RAMBlock *tmpblock; > > ram_addr_t offset = last_offset; > > + ram_addr_t tmpoffset; > > bool complete_round = false; > > int bytes_sent = 0; > > - MemoryRegion *mr; > > ram_addr_t dirty_ram_abs; /* Address of the start of the dirty page in > > ram_addr_t space */ > > + unsigned long hps = sysconf(_SC_PAGESIZE); > > > > - if (!block) > > + if (!block) { > > block = QTAILQ_FIRST(&ram_list.blocks); > > + last_was_from_queue = false; > > + } > > > > - while (true) { > > - mr = block->mr; > > - offset = migration_bitmap_find_and_reset_dirty(mr, offset, > > - &dirty_ram_abs); > > - if (complete_round && block == last_seen_block && > > - offset >= last_offset) { > > - break; > > + while (true) { /* Until we send a block or run out of stuff to send */ > > + tmpblock = NULL; > > + > > + /* > > + * Don't break host-page chunks up with queue items > > + * so only unqueue if, > > + * a) The last item came from the queue anyway > > + * b) The last sent item was the last target-page in a host page > > + */ > > + if (last_was_from_queue || !last_sent_block || > > + ((last_offset & (hps - 1)) == (hps - TARGET_PAGE_SIZE))) { > > + tmpblock = ram_save_unqueue_page(ms, &tmpoffset, &dirty_ram_abs); > > This test for whether we've completed a host page is pretty awkward. > I think it would be cleaner to have an inner loop / helper function > that completes sending an entire host page (whether requested or > scanned), before allowing the outer loop to even come back to here to > reconsider the queue. I've reworked that in the v7 series I've just posted; please see if it's more to your taste (I've not tested it on a machine with bigger pages yet though). (This patch is 32/42 in v7). Dave > > > } > > - if (offset >= block->used_length) { > > - offset = 0; > > - block = QTAILQ_NEXT(block, next); > > - if (!block) { > > - block = QTAILQ_FIRST(&ram_list.blocks); > > - complete_round = true; > > - ram_bulk_stage = false; > > + > > + if (tmpblock) { > > + /* We've got a block from the postcopy queue */ > > + trace_ram_find_and_save_block_postcopy(tmpblock->idstr, > > + (uint64_t)tmpoffset, > > + (uint64_t)dirty_ram_abs); > > + /* > > + * We're sending this page, and since it's postcopy nothing else > > + * will dirty it, and we must make sure it doesn't get sent again. > > + */ > > + if (!migration_bitmap_clear_dirty(dirty_ram_abs)) { > > + trace_ram_find_and_save_block_postcopy_not_dirty( > > + tmpblock->idstr, (uint64_t)tmpoffset, > > + (uint64_t)dirty_ram_abs, > > + test_bit(dirty_ram_abs >> TARGET_PAGE_BITS, ms->sentmap)); > > + > > + continue; > > } > > + /* > > + * As soon as we start servicing pages out of order, then we have > > + * to kill the bulk stage, since the bulk stage assumes > > + * in (migration_bitmap_find_and_reset_dirty) that every page is > > + * dirty, that's no longer true. > > + */ > > + ram_bulk_stage = false; > > + /* > > + * We mustn't change block/offset unless it's to a valid one > > + * otherwise we can go down some of the exit cases in the normal > > + * path. > > + */ > > + block = tmpblock; > > + offset = tmpoffset; > > + last_was_from_queue = true; > > Hrm. So now block can change during the execution of > ram_save_block(), which really suggests that splitting by block is no > longer a sensible subdivision of the loop surrounding ram_save_block. > I think it would make more sense to replace that entire surrounding > loop, so that the logic is essentially > > while (not finished) { > if (something is queued) { > send that > } else { > scan for an unsent block and offset > send that instead > } > > > > } else { > > - bytes_sent = ram_save_page(f, block, offset, last_stage); > > - > > - /* if page is unmodified, continue to the next */ > > - if (bytes_sent > 0) { > > - MigrationState *ms = migrate_get_current(); > > - if (ms->sentmap) { > > - set_bit(dirty_ram_abs >> TARGET_PAGE_BITS, ms->sentmap); > > + MemoryRegion *mr; > > + /* priority queue empty, so just search for something dirty */ > > + mr = block->mr; > > + offset = migration_bitmap_find_and_reset_dirty(mr, offset, > > + &dirty_ram_abs); > > + if (complete_round && block == last_seen_block && > > + offset >= last_offset) { > > + break; > > + } > > + if (offset >= block->used_length) { > > + offset = 0; > > + block = QTAILQ_NEXT(block, next); > > + if (!block) { > > + block = QTAILQ_FIRST(&ram_list.blocks); > > + complete_round = true; > > + ram_bulk_stage = false; > > } > > + continue; /* pick an offset in the new block */ > > + } > > + last_was_from_queue = false; > > + } > > > > - last_sent_block = block; > > - break; > > + /* We have a page to send, so send it */ > > + bytes_sent = ram_save_page(f, block, offset, last_stage); > > + > > + /* if page is unmodified, continue to the next */ > > + if (bytes_sent > 0) { > > + if (ms->sentmap) { > > + set_bit(dirty_ram_abs >> TARGET_PAGE_BITS, ms->sentmap); > > } > > + > > + last_sent_block = block; > > + break; > > } > > } > > last_seen_block = block; > > @@ -865,6 +968,7 @@ static void reset_ram_globals(void) > > last_offset = 0; > > last_version = ram_list.version; > > ram_bulk_stage = true; > > + last_was_from_queue = false; > > } > > > > #define MAX_WAIT 50 /* ms, half buffered_file limit */ > > diff --git a/trace-events b/trace-events > > index 8a0d70d..781cf5c 100644 > > --- a/trace-events > > +++ b/trace-events > > @@ -1217,6 +1217,8 @@ qemu_file_fclose(void) "" > > migration_bitmap_sync_start(void) "" > > migration_bitmap_sync_end(uint64_t dirty_pages) "dirty_pages %" PRIu64"" > > migration_throttle(void) "" > > +ram_find_and_save_block_postcopy(const char *block_name, uint64_t tmp_offset, uint64_t ram_addr) "%s/%" PRIx64 " ram_addr=%" PRIx64 > > +ram_find_and_save_block_postcopy_not_dirty(const char *block_name, uint64_t tmp_offset, uint64_t ram_addr, int sent) "%s/%" PRIx64 " ram_addr=%" PRIx64 " (sent=%d)" > > ram_postcopy_send_discard_bitmap(void) "" > > ram_save_queue_pages(const char *rbname, size_t start, size_t len) "%s: start: %zx len: %zx" > > > > -- > David Gibson | I'll have my music baroque, and my code > david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ > | _way_ _around_! > http://www.ozlabs.org/~dgibson -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK