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[188.85.120.92]) by smtp.gmail.com with ESMTPSA id l18-20020a5d4bd2000000b003078bb639bdsm13690727wrt.68.2023.05.10.10.57.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 May 2023 10:57:55 -0700 (PDT) From: Juan Quintela To: Andrei Gudkov Cc: , , , , Subject: Re: [PATCH v2 3/4] migration/calc-dirty-rate: added n-zero-pages metric In-Reply-To: (Andrei Gudkov's message of "Thu, 27 Apr 2023 15:42:59 +0300") References: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) Date: Wed, 10 May 2023 19:57:54 +0200 Message-ID: <871qjo6pct.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=170.10.133.124; envelope-from=quintela@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, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: , Reply-To: quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Andrei Gudkov wrote: > In sampling mode, a new metric is collected and reported: > number of pages entirely filled with zeroes. Good idea. > @@ -331,11 +336,20 @@ static uint32_t compute_page_hash(void *ptr) > v2 = QEMU_XXHASH_SEED + XXH_PRIME64_2; > v3 = QEMU_XXHASH_SEED + 0; > v4 = QEMU_XXHASH_SEED - XXH_PRIME64_1; > - for (i = 0; i < TARGET_PAGE_SIZE / 8; i += 4) { > - v1 = XXH64_round(v1, p[i + 0]); > - v2 = XXH64_round(v2, p[i + 1]); > - v3 = XXH64_round(v3, p[i + 2]); > - v4 = XXH64_round(v4, p[i + 3]); > + if (ptr) { It smells like a hack, that is only going to be used once in the program. But the only other option that I can think is repeating the function for the zero case. No way to win here. > + for (i = 0; i < TARGET_PAGE_SIZE / 8; i += 4) { > + v1 = XXH64_round(v1, p[i + 0]); > + v2 = XXH64_round(v2, p[i + 1]); > + v3 = XXH64_round(v3, p[i + 2]); > + v4 = XXH64_round(v4, p[i + 3]); > + } > + } else { > + for (i = 0; i < TARGET_PAGE_SIZE / 8; i += 4) { > + v1 = XXH64_round(v1, 0); > + v2 = XXH64_round(v2, 0); > + v3 = XXH64_round(v3, 0); > + v4 = XXH64_round(v4, 0); > + } > } > res = XXH64_mergerounds(v1, v2, v3, v4); > res += TARGET_PAGE_SIZE; > @@ -343,6 +357,17 @@ static uint32_t compute_page_hash(void *ptr) > return (uint32_t)(res & UINT32_MAX); > } > > +static uint32_t get_zero_page_hash(void) > +{ > + static uint32_t hash; > + static int is_computed; bool? Later, Juan.