From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Christie Subject: Re: [PATCH 04/16] scsi_dh_alua: Make stpg synchronous Date: Wed, 12 Feb 2014 10:11:12 -0600 Message-ID: <52FB9D20.5060900@cs.wisc.edu> References: <1391160600-19652-1-git-send-email-hare@suse.de> <1391160600-19652-5-git-send-email-hare@suse.de> <52F435B3.3090600@cs.wisc.edu> <52F43CD7.5050900@cs.wisc.edu> <52FB9353.7040807@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from sabe.cs.wisc.edu ([128.105.6.20]:52889 "EHLO sabe.cs.wisc.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751948AbaBLQLl (ORCPT ); Wed, 12 Feb 2014 11:11:41 -0500 In-Reply-To: <52FB9353.7040807@suse.de> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Hannes Reinecke Cc: James Bottomley , Sean Stewart , Martin George , linux-scsi@vger.kernel.org On 2/12/14 9:29 AM, Hannes Reinecke wrote: > On 02/07/2014 02:54 AM, Mike Christie wrote: >> On 02/06/2014 07:24 PM, Mike Christie wrote: >>> On 01/31/2014 03:29 AM, Hannes Reinecke wrote: >>>> We should be issuing STPG synchronously as we need to >>>> evaluate the return code on failure. >>>> >>>> Signed-off-by: Hannes Reinecke >>> >>> I think we need to also make dm-mpath.c use a non-ordered workqueue for >>> kmpath_handlerd. With this patch and the current ordered workqueue in >>> dm-mpath I think we will only be able to do one STPG at a time. I think >>> if we use a normal old non-ordered workqueue then we would be limited to >>> have max_active STPGs executing. >> >> I goofed and commented in the order I saw the patches :) I take this >> comment back for this patch, because I see in 16/16 you added a new >> workqueue to scsi_dh_alua to do rtpgs and stpgs. >> >> For 16/16 though, do we want to make kmpath_aluad a non single threaded >> workqueue? It looks like max_active for single threaded is only one work >> at a time too. >> > Well, that was by intention. > > The workqueue will be triggered very infrequently (basically for > every path switch). > For implicit ALUA we just need to issue a RTPG to get the new path > status; there we might be suffering from single threaded behaviour. > But we need to issue it only once and it should be processed > reasonably fast. > For explicit ALUA we'll have to send an STPG, which has potentially > system-wide implications. So sending several to (supposedly) > different targets might actually be contraproductive, as the first > might have already set the status for the second call. > Here we most definitely _want_ serialisation to avoid superfluous STPGs. > What target is this? For our target it adds a regression. It only affects devices on the same port group. We then have multiple groups. Before the patch, we could failover/failback multiple devices in parallel. To do 64 devices it took about 3 seconds. With your patch it takes around 3 minutes.