From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Gross Subject: Re: [Xen-devel] [PATCH 1/4] Add XEN pvSCSI protocol description Date: Mon, 30 Jun 2014 13:18:48 +0200 Message-ID: <53B14798.70303@suse.com> References: <1403879676-25431-1-git-send-email-jgross@suse.com> <1403879676-25431-2-git-send-email-jgross@suse.com> <20140627171154.GA30451@laptop.dumpdata.com> <53B15FFA020000780001E79E@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from cantor2.suse.de ([195.135.220.15]:41148 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751241AbaF3LSw (ORCPT ); Mon, 30 Jun 2014 07:18:52 -0400 In-Reply-To: <53B15FFA020000780001E79E@mail.emea.novell.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Jan Beulich , Konrad Rzeszutek Wilk Cc: Juergen Gross , linux-scsi@vger.kernel.org, JBottomley@parallels.com, xen-devel@lists.xen.org On 06/30/2014 01:02 PM, Jan Beulich wrote: >>>> On 27.06.14 at 19:11, wrote: >> On Fri, Jun 27, 2014 at 04:34:33PM +0200, jgross@suse.com wrote: >>> +/* >>> + * Maximum scatter/gather segments per request. >>> + * >>> + * Considering balance between allocating at least 16 "vscsiif_req= uest" >>> + * structures on one page (4096 bytes) and the number of scatter/g= ather >>> + * elements needed, we decided to use 26 as a magic number. >>> + */ >>> +#define VSCSIIF_SG_TABLESIZE 26 >>> + >>> +/* >>> + * based on Linux kernel 2.6.18 >> >> This being a bit more .. new, - do these sizes make sense anymore? >> Should they be extended a bit? Or have support for using the >> old ones (as default) and then negotiate new sizes with the kernel? >> (If of course there is a difference?) > > As J=C3=BCrgen already said (and as you should have noticed yourself)= - > this is an interface definition that we can't just change. Negotiatio= n > of larger counts is an option, which is what VSCSIIF_ACT_SCSI_SG_PRES= ET > is intended for (the implementation of which isn't part of this patch= set > afaics, but could be made available on top of it). I don't think this is the proper way to handle larger SG lists. The VSCSIIF_ACT_SCSI_SG_PRESET option would just bump the maximum length up to 31 (currently 26). Or was it thought to be incremental (multiple presets for one request)? I'd rather add a way to specify SG lists residing in an own (granted) page (or even multiple pages). This would allow 512*26 SG entries without having to change the request structure. The capability to handle this feature could be indicated via xenstore. > Most if not all of your other comments are a little questionable too > in this context - any parts you aren't happy about would really > better be addressed towards the canonical header in the Xen tree. > (I know you had other interface headers diverge too in their Linux > incarnation, but personally I don't think this is an appropriate thin= g > to do, perhaps apart for pure coding style adjustments.) Juergen -- 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