From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomas Henzl Subject: Re: [PATCH 8/9] scsi: megaraid_sas - Driver take some workloads from FW Date: Tue, 30 Nov 2010 16:57:38 +0100 Message-ID: <4CF51EF2.1010606@redhat.com> References: <4B6A08C587958942AA3002690DD4F8C3D0804533@cosmail02.lsi.com> <4B6A08C587958942AA3002690DD4F8C3DBD67F68@cosmail02.lsi.com> <4B6A08C587958942AA3002690DD4F8C30106A961BD@cosmail02.lsi.com> <4B6A08C587958942AA3002690DD4F8C30106A961D6@cosmail02.lsi.com> <4B6A08C587958942AA3002690DD4F8C30106A961E4@cosmail02.lsi.com> <4B6A08C587958942AA3002690DD4F8C30106A961F2@cosmail02.lsi.com> <4B6A08C587958942AA3002690DD4F8C30106A96213@cosmail02.lsi.com> <4B6A08C587958942AA3002690DD4F8C30106A96218@cosmail02.lsi.com> <4B6A08C587958942AA3002690DD4F8C30106A9621E@cosmail02.lsi.com> <4B6A08C587958942AA3002690DD4F8C30106A96223@cosmail02.lsi.com> <1290189181.23556.77.camel@mulgrave.site> <4B6A08C587958942AA3002690DD4F8C30106B1DEB9@cosmail02.lsi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <4B6A08C587958942AA3002690DD4F8C30106B1DEB9@cosmail02.lsi.com> Sender: linux-kernel-owner@vger.kernel.org To: "Yang, Bo" Cc: James Bottomley , "'linux-scsi@vger.kernel.org'" , "'akpm@osdl.org'" , "'linux-kernel@vger.kernel.org'" , "Daftardar, Jayant" , "Prabhakaran, Rajesh" List-Id: linux-scsi@vger.kernel.org On 11/24/2010 04:22 PM, Yang, Bo wrote: > James, > > Our megaraid sas driver only implemented the part of the XOR calculat= ion and copy capability(moving data between 2 buffers) for the RAID5 cm= ds which FW asks driver to do. When fw received very heavy I/Os and th= ere are high pending cmds in FW, fw will ask the help from driver to fi= nish some cmds and reduce the fw heavy load. Driver will only do part = of the RAID5 (not take the jobs) from FW. Driver is not duplicating Pa= rity calculation done on dm/md. > =20 Do I understand it right - it means that the computation is done someti= mes in the firmware and sometimes in the driver depending on the load? I think it is not good h= aving two complicated computations on two different places. Wouldn't it better to compute it = always in the driver? Could we get a module option for choosing this computation - a)automati= c, b)only in fw c)only in driver? Tomas > Thanks, > > Bo Yang =20 > > > > -----Original Message----- > From: James Bottomley [mailto:James.Bottomley@HansenPartnership.com]=20 > Sent: Friday, November 19, 2010 12:53 PM > To: Yang, Bo > Cc: 'linux-scsi@vger.kernel.org'; 'akpm@osdl.org'; 'linux-kernel@vger= =2Ekernel.org'; Tomas Henzl > Subject: Re: [PATCH 8/9] scsi: megaraid_sas - Driver take some worklo= ads from FW > > On Fri, 2010-11-19 at 10:43 -0700, Yang, Bo wrote: > =20 >> Driver added the new feature to take some of the workloads from FW t= o increase >> performance of the iMR controller. FW assigns the read cmds back to= driver >> which will increase the performance for megaraid sas iMR controller. >> =20 > Just on a process note: you don't have to cc me at every known > address ... I do read linux-scsi ... > > My first take on this patch is that you're basically passing data bac= k > to the kernel for RAID-N parity calculations. This effectively makes > your RAID one of those pseudo HW ones. In which case, why not simply > abandon the HW raid piece and have it all done by DM/MD, which are we= ll > optimised for all types of RAID? The reason for asking is that we're > trying to reduce the number of in-kernel raid implementations and thi= s > is going in the wrong direction. > > James > > > N=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BDr=EF=BF=BD=EF=BF=BDy=EF= =BF=BD=EF=BF=BD=EF=BF=BDb=EF=BF=BDX=EF=BF=BD=EF=BF=BD=C7=A7v=EF=BF=BD^=EF= =BF=BD)=DE=BA{.n=EF=BF=BD+=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD{=EF=BF=BD= =EF=BF=BD=EF=BF=BD"=EF=BF=BD{ay=EF=BF=BD=1D=CA=87=DA=99=EF=BF=BD,j=07=EF= =BF=BD=EF=BF=BDf=EF=BF=BD=EF=BF=BD=EF=BF=BDh=EF=BF=BD=EF=BF=BD=EF=BF=BD= z=EF=BF=BD=1E=EF=BF=BDw=EF=BF=BD=EF=BF=BD=EF=BF=BD=0C=EF=BF=BD=EF=BF=BD= =EF=BF=BDj:+v=EF=BF=BD=EF=BF=BD=EF=BF=BDw=EF=BF=BDj=EF=BF=BDm=EF=BF=BD=EF= =BF=BD=EF=BF=BD=EF=BF=BD=07=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BDzZ+=EF=BF= =BD=EF=BF=BD=DD=A2j"=EF=BF=BD=EF=BF=BD!tml=3D