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[70.31.27.79]) by smtp.gmail.com with ESMTPSA id i1-20020ac813c1000000b0035c1e18762csm12334514qtj.84.2022.10.04.11.24.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Oct 2022 11:24:36 -0700 (PDT) From: Peter Xu To: qemu-devel@nongnu.org Cc: "Daniel P . Berrange" , Leonardo Bras Soares Passos , "Dr . David Alan Gilbert" , peterx@redhat.com, Juan Quintela Subject: [PATCH v2 4/5] migration: Use non-atomic ops for clear log bitmap Date: Tue, 4 Oct 2022 14:24:29 -0400 Message-Id: <20221004182430.97638-5-peterx@redhat.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20221004182430.97638-1-peterx@redhat.com> References: <20221004182430.97638-1-peterx@redhat.com> MIME-Version: 1.0 Content-type: text/plain Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=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: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Since we already have bitmap_mutex to protect either the dirty bitmap or the clear log bitmap, we don't need atomic operations to set/clear/test on the clear log bitmap. Switching all ops from atomic to non-atomic versions, meanwhile touch up the comments to show which lock is in charge. Introduced non-atomic version of bitmap_test_and_clear_atomic(), mostly the same as the atomic version but simplified a few places, e.g. dropped the "old_bits" variable, and also the explicit memory barriers. Reviewed-by: Dr. David Alan Gilbert Signed-off-by: Peter Xu --- include/exec/ram_addr.h | 11 +++++----- include/exec/ramblock.h | 3 +++ include/qemu/bitmap.h | 1 + util/bitmap.c | 45 +++++++++++++++++++++++++++++++++++++++++ 4 files changed, 55 insertions(+), 5 deletions(-) diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h index f3e0c78161..5092a2e0ff 100644 --- a/include/exec/ram_addr.h +++ b/include/exec/ram_addr.h @@ -42,7 +42,8 @@ static inline long clear_bmap_size(uint64_t pages, uint8_t shift) } /** - * clear_bmap_set: set clear bitmap for the page range + * clear_bmap_set: set clear bitmap for the page range. Must be with + * bitmap_mutex held. * * @rb: the ramblock to operate on * @start: the start page number @@ -55,12 +56,12 @@ static inline void clear_bmap_set(RAMBlock *rb, uint64_t start, { uint8_t shift = rb->clear_bmap_shift; - bitmap_set_atomic(rb->clear_bmap, start >> shift, - clear_bmap_size(npages, shift)); + bitmap_set(rb->clear_bmap, start >> shift, clear_bmap_size(npages, shift)); } /** - * clear_bmap_test_and_clear: test clear bitmap for the page, clear if set + * clear_bmap_test_and_clear: test clear bitmap for the page, clear if set. + * Must be with bitmap_mutex held. * * @rb: the ramblock to operate on * @page: the page number to check @@ -71,7 +72,7 @@ static inline bool clear_bmap_test_and_clear(RAMBlock *rb, uint64_t page) { uint8_t shift = rb->clear_bmap_shift; - return bitmap_test_and_clear_atomic(rb->clear_bmap, page >> shift, 1); + return bitmap_test_and_clear(rb->clear_bmap, page >> shift, 1); } static inline bool offset_in_ramblock(RAMBlock *b, ram_addr_t offset) diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h index 6cbedf9e0c..adc03df59c 100644 --- a/include/exec/ramblock.h +++ b/include/exec/ramblock.h @@ -53,6 +53,9 @@ struct RAMBlock { * and split clearing of dirty bitmap on the remote node (e.g., * KVM). The bitmap will be set only when doing global sync. * + * It is only used during src side of ram migration, and it is + * protected by the global ram_state.bitmap_mutex. + * * NOTE: this bitmap is different comparing to the other bitmaps * in that one bit can represent multiple guest pages (which is * decided by the `clear_bmap_shift' variable below). On diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h index 82a1d2f41f..3ccb00865f 100644 --- a/include/qemu/bitmap.h +++ b/include/qemu/bitmap.h @@ -253,6 +253,7 @@ void bitmap_set(unsigned long *map, long i, long len); void bitmap_set_atomic(unsigned long *map, long i, long len); void bitmap_clear(unsigned long *map, long start, long nr); bool bitmap_test_and_clear_atomic(unsigned long *map, long start, long nr); +bool bitmap_test_and_clear(unsigned long *map, long start, long nr); void bitmap_copy_and_clear_atomic(unsigned long *dst, unsigned long *src, long nr); unsigned long bitmap_find_next_zero_area(unsigned long *map, diff --git a/util/bitmap.c b/util/bitmap.c index f81d8057a7..8d12e90a5a 100644 --- a/util/bitmap.c +++ b/util/bitmap.c @@ -240,6 +240,51 @@ void bitmap_clear(unsigned long *map, long start, long nr) } } +bool bitmap_test_and_clear(unsigned long *map, long start, long nr) +{ + unsigned long *p = map + BIT_WORD(start); + const long size = start + nr; + int bits_to_clear = BITS_PER_LONG - (start % BITS_PER_LONG); + unsigned long mask_to_clear = BITMAP_FIRST_WORD_MASK(start); + bool dirty = false; + + assert(start >= 0 && nr >= 0); + + /* First word */ + if (nr - bits_to_clear > 0) { + if ((*p) & mask_to_clear) { + dirty = true; + } + *p &= ~mask_to_clear; + nr -= bits_to_clear; + bits_to_clear = BITS_PER_LONG; + p++; + } + + /* Full words */ + if (bits_to_clear == BITS_PER_LONG) { + while (nr >= BITS_PER_LONG) { + if (*p) { + dirty = true; + *p = 0; + } + nr -= BITS_PER_LONG; + p++; + } + } + + /* Last word */ + if (nr) { + mask_to_clear &= BITMAP_LAST_WORD_MASK(size); + if ((*p) & mask_to_clear) { + dirty = true; + } + *p &= ~mask_to_clear; + } + + return dirty; +} + bool bitmap_test_and_clear_atomic(unsigned long *map, long start, long nr) { unsigned long *p = map + BIT_WORD(start); -- 2.37.3