On 18-11-09 15:14:35, Alexander Duyck wrote: > On Fri, 2018-11-09 at 16:15 -0500, Pavel Tatashin wrote: > > On 18-11-05 13:19:25, Alexander Duyck wrote: > > > This patchset is essentially a refactor of the page initialization logic > > > that is meant to provide for better code reuse while providing a > > > significant improvement in deferred page initialization performance. > > > > > > In my testing on an x86_64 system with 384GB of RAM and 3TB of persistent > > > memory per node I have seen the following. In the case of regular memory > > > initialization the deferred init time was decreased from 3.75s to 1.06s on > > > average. For the persistent memory the initialization time dropped from > > > 24.17s to 19.12s on average. This amounts to a 253% improvement for the > > > deferred memory initialization performance, and a 26% improvement in the > > > persistent memory initialization performance. > > > > Hi Alex, > > > > Please try to run your persistent memory init experiment with Daniel's > > patches: > > > > https://lore.kernel.org/lkml/20181105165558.11698-1-daniel.m.jordan@xxxxxxxxxx/ > > I've taken a quick look at it. It seems like a bit of a brute force way > to try and speed things up. I would be worried about it potentially There is a limit to max number of threads that ktasks start. The memory throughput is *much* higher than what one CPU can maxout in a node, so there is no reason to leave the other CPUs sit idle during boot when they can help to initialize. > introducing performance issues if the number of CPUs thrown at it end > up exceeding the maximum throughput of the memory. > > The data provided with patch 11 seems to point to issues such as that. > In the case of the E7-8895 example cited it is increasing the numbers > of CPUs used from memory initialization from 8 to 72, a 9x increase in > the number of CPUs but it is yeilding only a 3.88x speedup. Yes, but in both cases we are far from maxing out the memory throughput. The 3.88x is indeed low, and I do not know what slows it down. Daniel, Could you please check why multi-threading efficiency is so low here? I bet, there is some atomic operation introduces a contention within a node. It should be possible to resolve. > > > The performance should improve by much more than 26%. > > The 26% improvement, or speedup of 1.26x using the ktask approach, was > for persistent memory, not deferred memory init. The ktask patch > doesn't do anything for persistent memory since it is takes the hot- > plug path and isn't handled via the deferred memory init. Ah, I thought in your experiment persistent memory takes deferred init path. So, what exactly in your patches make this 1.26x speedup? > > I had increased deferred memory init to about 3.53x the original speed > (3.75s to 1.06s) on the system which I was testing. I do agree the two > patches should be able to synergistically boost each other though as > this patch set was meant to make the init much more cache friendly so > as a result it should scale better as you add additional cores. I know > I had done some playing around with fake numa to split up a single node > into 8 logical nodes and I had seen a similar speedup of about 3.85x > with my test memory initializing in about 275ms. > > > Overall, your works looks good, but it needs to be considered how easy it will be > > to merge with ktask. I will try to complete the review today. > > > > Thank you, > > Pasha > > Looking over the patches they are still in the RFC stage and the data > is in need of updates since it is referencing 4.15-rc kernels as its > baseline. If anything I really think the ktask patch 11 would be easier > to rebase around my patch set then the other way around. Also, this > series is in Andrew's mmots as of a few days ago, so I think it will be > in the next mmotm that comes out. I do not disagree, I think these two patch series should complement each other. But, if your changes make it impossible for ktask, I would strongly argue against it, as the potential improvements with ktasks are much higher. But, so far I do not see anything, so I think they can work together. I am still reviewing your work. > > The integration with the ktask code should be pretty straight forward. > If anything I think my code would probably make it easier since it gets > rid of the need to do all this in two passes. The only new limitation > it would add is that you would probably want to split up the work along > either max order or section aligned boundaries. What it would Which is totally OK, it should make ktasks scale even better. > essentially do is make things so that each of the ktask threads would > probably look more like deferred_grow_zone which after my patch set is > actually a fairly simple function. > > Thanks. Thank you, Pasha
