On 10/01/2020 23:50, Rob Herring wrote: > On Tue, Jan 7, 2020 at 4:22 AM Jon Hunter <jonathanh@xxxxxxxxxx> wrote: >> >> Hi Rob, >> >> On 11/12/2019 23:23, Rob Herring wrote: >>> The phandle cache was added to speed up of_find_node_by_phandle() by >>> avoiding walking the whole DT to find a matching phandle. The >>> implementation has several shortcomings: >>> >>> - The cache is designed to work on a linear set of phandle values. >>> This is true for dtc generated DTs, but not for other cases such as >>> Power. >>> - The cache isn't enabled until of_core_init() and a typical system >>> may see hundreds of calls to of_find_node_by_phandle() before that >>> point. >>> - The cache is freed and re-allocated when the number of phandles >>> changes. >>> - It takes a raw spinlock around a memory allocation which breaks on >>> RT. >>> >>> Change the implementation to a fixed size and use hash_32() as the >>> cache index. This greatly simplifies the implementation. It avoids >>> the need for any re-alloc of the cache and taking a reference on nodes >>> in the cache. We only have a single source of removing cache entries >>> which is of_detach_node(). >>> >>> Using hash_32() removes any assumption on phandle values improving >>> the hit rate for non-linear phandle values. The effect on linear values >>> using hash_32() is about a 10% collision. The chances of thrashing on >>> colliding values seems to be low. >>> >>> To compare performance, I used a RK3399 board which is a pretty typical >>> system. I found that just measuring boot time as done previously is >>> noisy and may be impacted by other things. Also bringing up secondary >>> cores causes some issues with measuring, so I booted with 'nr_cpus=1'. >>> With no caching, calls to of_find_node_by_phandle() take about 20124 us >>> for 1248 calls. There's an additional 288 calls before time keeping is >>> up. Using the average time per hit/miss with the cache, we can calculate >>> these calls to take 690 us (277 hit / 11 miss) with a 128 entry cache >>> and 13319 us with no cache or an uninitialized cache. >>> >>> Comparing the 3 implementations the time spent in >>> of_find_node_by_phandle() is: >>> >>> no cache: 20124 us (+ 13319 us) >>> 128 entry cache: 5134 us (+ 690 us) >>> current cache: 819 us (+ 13319 us) >>> >>> We could move the allocation of the cache earlier to improve the >>> current cache, but that just further complicates the situation as it >>> needs to be after slab is up, so we can't do it when unflattening (which >>> uses memblock). >>> >>> Reported-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> >>> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> >>> Cc: Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx> >>> Cc: Frank Rowand <frowand.list@xxxxxxxxx> >>> Signed-off-by: Rob Herring <robh@xxxxxxxxxx> >> >> With next-20200106 I have noticed a regression on Tegra210 where it >> appears that only one of the eMMC devices is being registered. Bisect is >> pointing to this patch and reverting on top of next fixes the problem. >> That is as far as I have got so far, so if you have any ideas, please >> let me know. Unfortunately, there do not appear to be any obvious errors >> from the bootlog. > > I guess that's tegra210-p2371-2180.dts because none of the others have > 2 SD hosts enabled. I don't see anything obvious though. Are you doing > any runtime mods to the DT? I have noticed that the bootloader is doing some runtime mods and so checking if this is the cause. I will let you know, but most likely, seeing as I cannot find anything wrong with this change itself. Cheers Jon -- nvpublic
