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 10:26:59 -0600 Message-ID: <52FBA0D3.50907@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> <52FB9D20.5060900@cs.wisc.edu> 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]:52920 "EHLO sabe.cs.wisc.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752412AbaBLQ1K (ORCPT ); Wed, 12 Feb 2014 11:27:10 -0500 In-Reply-To: <52FB9D20.5060900@cs.wisc.edu> 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 10:11 AM, Mike Christie wrote: > 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. > Also, with your pg change patch, I think we can serialize based on group and it will do what you want and also allow us to do STPGs to different groups in parallel.