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[80.39.130.236]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-442cd3af15bsm74544145e9.30.2025.05.09.07.21.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 09 May 2025 07:21:46 -0700 (PDT) Message-ID: Date: Fri, 9 May 2025 16:21:45 +0200 Precedence: bulk X-Mailing-List: dm-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH] multipath-tools: replace round-robin path selector with the default for NFINIDAT/InfiniBox To: Martin Wilck , arnony@infinidat.com Cc: Benjamin Marzinski , Christophe Varoqui , DM-DEVEL ML , John Meneghini References: <20250509134459.226640-1-xose.vazquez@gmail.com> <085c156c31fcd2fc5da4e889642bd6186c677a7c.camel@suse.com> Content-Language: en-US, en-GB, es-ES From: Xose Vazquez Perez In-Reply-To: <085c156c31fcd2fc5da4e889642bd6186c677a7c.camel@suse.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 5/9/25 4:08 PM, Martin Wilck wrote: > Please support this claim with actual numbers. I'm not saying that it's > wrong (it makes sense that John's argument "the round-robin path > selector is inefficient in cases where there is a difference in latency > between paths" applies to all implementations), but you can't present > numbers for one technology and simply apply them to a different > technology without providing any evidence for the latter. > > I'd accept this statement in a weaker form, like "It is reasonable to > assume that the same effects would be measured with dm-multipath over > SCSI devices, too". Marzinski did some tests time ago: git show c015b1281 commit c015b128103e7a6426d124a38cd679a181573b88 Author: Benjamin Marzinski Date: Sat Jan 12 00:04:40 2013 -0600 multipath: change default path_selector to My testing has showed service-time to be as good and occassionally noticeably better than round-robin. So the patch switches the default selector to give better performance out of the box. Signed-off-by: Benjamin Marzinski diff --git a/libmultipath/defaults.h b/libmultipath/defaults.h index f647ee08..097c66f7 100644 --- a/libmultipath/defaults.h +++ b/libmultipath/defaults.h @@ -1,7 +1,7 @@ #define DEFAULT_UID_ATTRIBUTE "ID_SERIAL" #define DEFAULT_UDEVDIR "/dev" #define DEFAULT_MULTIPATHDIR "/" LIB_STRING "/multipath" -#define DEFAULT_SELECTOR "round-robin 0" +#define DEFAULT_SELECTOR "service-time 0" #define DEFAULT_ALIAS_PREFIX "mpath" #define DEFAULT_FEATURES "0" #define DEFAULT_HWHANDLER "0" I didn't do any test, sorry.