On Wed, 25 Nov 2015, Nick Fisk wrote: > Hi Sage > > > -----Original Message----- > > From: Sage Weil [mailto:sage@xxxxxxxxxxxx] > > Sent: 25 November 2015 17:38 > > To: Nick Fisk <nick@xxxxxxxxxx> > > Cc: 'ceph-users' <ceph-users@xxxxxxxxxxxxxx>; ceph-devel@xxxxxxxxxxxxxxx; > > 'Mark Nelson' <mnelson@xxxxxxxxxx> > > Subject: Re: Cache Tiering Investigation and Potential Patch > > > > On Wed, 25 Nov 2015, Nick Fisk wrote: > > > Presentation from the performance meeting. > > > > > > I seem to be unable to post to Ceph-devel, so can someone please > > > repost there if useful. > > > > Copying ceph-devel. The problem is just that your email is HTML-formatted. > > If you send it in plaintext vger won't reject it. > > Right ok, let's see if this gets through. > > > > > > I will try and get a PR sorted, I realise that this change modifies > > > the way the cache was originally designed but I think it provides a > > > quick win for the performance increase involved. If there are plans > > > for a better solution in time for the next release, then I would be > > > really interested in working to that goal instead. > > > > It's how it was intended/documented to work, so I think this falls in the 'bug > > fix' category. I did a quick PR here: > > > > https://github.com/ceph/ceph/pull/6702 > > > > Does that look right? > > Yes I think that should definitely be an improvement. I can't quite get > my head around how it will perform in instances where you miss 1 hitset > but all others are a hit. Like this: > > H H H M H H H H H H H H > > And recency is set to 8 for example. It maybe that it doesn't have much > effect on the overall performance. It might be that there is a strong > separation of really hot blocks and hot blocks, but this could turn out > to be a good thing. Yeah... In the above case recency 3 would be enough (or 9, depending on whether that's chronological or reverse chronological order). Doing an N out of M or similar is a bit more flexible and probably something we should add on top. (Or, we could change recency to be N/M instead of just N.) > Would it be useful for me to run all 3 versions (Old, this and mine) > through the same performance test I did before? If you have time, sure! At the very least it'd be great to see the new version go through the same test. > Also I saw pull request 6623, is it still relevant to get the list order > right? Oh right, I forgot about that one. I'll incorporate that fix and then you can test that version. Thanks! sage -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
