From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Reinecke Subject: Re: [PATCH 04/16] scsi_dh_alua: Make stpg synchronous Date: Wed, 12 Feb 2014 16:29:23 +0100 Message-ID: <52FB9353.7040807@suse.de> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from cantor2.suse.de ([195.135.220.15]:44459 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751530AbaBLP3Y (ORCPT ); Wed, 12 Feb 2014 10:29:24 -0500 In-Reply-To: <52F43CD7.5050900@cs.wisc.edu> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Mike Christie Cc: James Bottomley , Sean Stewart , Martin George , linux-scsi@vger.kernel.org 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 i= n >> dm-mpath I think we will only be able to do one STPG at a time. I th= ink >> if we use a normal old non-ordered workqueue then we would be limite= d to >> have max_active STPGs executing. >=20 > 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. >=20 > For 16/16 though, do we want to make kmpath_aluad a non single thread= ed > workqueue? It looks like max_active for single threaded is only one w= ork > at a time too. >=20 Well, that was by intention. The workqueue will be triggered very infrequently (basically for every path switch). =46or 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. =46or 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= =2E So for now I think we can stick with the single threaded workqueue, and can revise this later if it's found to be a scalability issue. Cheers, Hannes --=20 Dr. Hannes Reinecke zSeries & Storage hare@suse.de +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=FCrnberg GF: J. Hawn, J. Guild, F. Imend=F6rffer, HRB 16746 (AG N=FCrnberg) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html