On 2011-06-10 10:30, tao.peng@xxxxxxx wrote: > > -----Original Message----- > From: linux-nfs-owner@xxxxxxxxxxxxxxx [mailto:linux-nfs-owner@xxxxxxxxxxxxxxx] On Behalf Of Benny Halevy > Sent: Friday, June 10, 2011 8:48 PM > To: Peng, Tao > Cc: bergwolf@xxxxxxxxx; rees@xxxxxxxxx; linux-nfs@xxxxxxxxxxxxxxx; honey@xxxxxxxxxxxxxx > Subject: Re: [PATCH 87/88] Add configurable prefetch size for layoutget > > On 2011-06-10 02:02, tao.peng@xxxxxxx wrote: >> Hi, Benny, >> >> Cheers, >> -Bergwolf >> >> >> -----Original Message----- >> From: linux-nfs-owner@xxxxxxxxxxxxxxx [mailto:linux-nfs-owner@xxxxxxxxxxxxxxx] On Behalf Of Benny Halevy >> Sent: Friday, June 10, 2011 5:30 AM >> To: Peng Tao >> Cc: Jim Rees; linux-nfs@xxxxxxxxxxxxxxx; peter honeyman >> Subject: Re: [PATCH 87/88] Add configurable prefetch size for layoutget >> >> On 2011-06-09 07:54, Peng Tao wrote: >>> On Thu, Jun 9, 2011 at 2:06 PM, Benny Halevy <bhalevy@xxxxxxxxxxx> wrote: >>>> On 2011-06-08 03:15, Peng Tao wrote: >>>>> On 6/8/11, Jim Rees <rees@xxxxxxxxx> wrote: >>>>>> Benny Halevy wrote: >>>>>> >>>>>> NAK. >>>>>> This affects all layout types. In particular it is undesired >>>>>> for write layouts that extend the file with the objects layout. >>>>>> The server can extend the layout segments range >>>>>> over what the client requested so why would the client >>>>>> ask for artificially large layouts? >>>>>> >>>>>> This has actually been the subject of some debate over Thursday night >>>>>> beers. The problem we're trying to solve is that the client is spending 98% >>>>>> of its time in layoutget. This patch gives us something like a 10x >>>>>> speedup. But many of us think it's not the right fix. I suggest we discuss >>>>>> next week. >>>>>> >>>> >>>> Sure. >>>> >>>>>> But note that this patch doesn't change anything unless you set the sysctl. >>>>> there is a default value of 2M. maybe we can set it to page size by >>>>> default so other layout are not affected and block layout can let >>>>> users set it by hand if they care about performance. does this make >>>>> sense? >>>> >>>> If doing it at all why use a sysctl rather than a mount option? >>> The purpose of using a sysctl is to give client the ability to change >>> it on the fly. In theory, layout prefetching can benefit all layout >>> types. So the patch tries to solve it in the pnfs generic layer. >>> >> >> But the need for this varies per-server and many times per application. >> Think sequential vs. random I/O. Therefore a mount option would help >> tuning the behavior on a per-use basis. Global behavior must be implemented >> using a dynamic algorithm that would take both the workload and the server >> observed behavior into account. >> [PT] Indeed. Dynamic algorithm is supposed to be able to solve all this. And it often takes longer to be designed/accepted. It has to prove to be better in most scenarios and does not hurt the left. > > We need to find an acceptable solution to push this driver upstream. > I understand that developing a dynamic algorithm in the given time frame is > too big of a challenge, but hacking yet another client tunable is out of the > question either. For testing in the Bakeathon I'd consider taking a DEVONLY version > of this patch that is enabled using a config option and defaults to zero to have no effect > in run-time until the sysctl is sets it differently. > But keep in mind this is not suitable for pushing upstream. > [PT] Thanks for your understanding. We truly want to solve the performance problem and are open to suggestions. And this will be a feature that benefits all layout types, am I right? Adaptive layout prefetching at the client side is a nice workaround for naive server implementations but you can't get around implementing a more sophisticated algorithm on the server side. As for the benefit, if yo implement such an algorithm, on the client side I would like it to be implemented generically so that all layout types could benefit from it. Benny > > -Tao -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
