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Greetings, We present “Machine Function Splitter”, a codegen optimization pass which splits functions into hot and cold parts. This pass leverages the basic block sections feature recently introduced in LLVM from the Propeller project. The pass targets functions with profile coverage, identifies cold blocks and moves them to a separate section. The linker groups all cold blocks across functions together, decreasing...

...; > On Feb 5, 2019, at 2:38 PM, Teresa Johnson via llvm-dev < > llvm-dev at lists.llvm.org> wrote: > > > > > On Mon, Jan 28, 2019 at 11:03 AM Aditya K via llvm-dev < > llvm-dev at lists.llvm.org> wrote: > >> > The splitting pass currently doesn’t move cold symbols into a separate >> section. Is that affecting your results? >> Maybe partly, the main reason is that, in the absence of good profile >> info, we aren't finding many cold blocks. >> > > We noticed that the split cold functions are ending up in the regular &g...

The splitting pass currently doesn’t move cold symbols into a separate section. Is that affecting your results? On Darwin, we plan on using a symbol attribute to provide an ordering hint to the linker (see r352227, N_COLD_FUNC). vedant > On Jan 28, 2019, at 10:51 AM, Aditya K via llvm-dev <llvm-dev at lists.llvm.org> wrote: > &g...

Hello, I’d like to give a status update to the community about the recently-added hot/cold splitting pass. I'll provide some motivation for the pass, describe its implementation, summarize recent/ongoing work, and share early results. # Motivation We (at Apple) have found that memory pressure from resident pages of code is significant on embedded devices. In particular, this pressu...

On Mon, Jan 28, 2019 at 11:03 AM Aditya K via llvm-dev < llvm-dev at lists.llvm.org> wrote: > > The splitting pass currently doesn’t move cold symbols into a separate > section. Is that affecting your results? > Maybe partly, the main reason is that, in the absence of good profile > info, we aren't finding many cold blocks. > We noticed that the split cold functions are ending up in the regular .text section instead of .t...

Hello, I am Ruijie Fang, a GSoC student working on "Improve hot cold splitting to aggressively outline small blocks." Over the course of last week, I met with my mentor and co-mentor, Aditya Kumar, and Rodrigo Rocha, and we made a preliminary plan on improving the existing hot/cold splitting pass in LLVM through identifying patterns of cold blocks in real-world...

>Exceptions >All eh pads are grouped together regardless of their coldness and are part of the original function. There are outstanding issues with splitting eh pads if they reside in separate sections in the binary. This remains as part of future work. Can you elaborate more on the outstanding issues with splitting eh pads? From my dip into the unwind map in gc...

...lar. Cost model can sometimes be quite tricky though -- it is hard to compare the cost with the actual benefit brought by the splitting. The beauty of machine splitting is that it does not depend on sophisticated cost/benefit model. > > In contrast, the machine function splitter extracts cold code into a separate > section. > HCS also adds a section prefix to all the cold functions. It is possible > that the cold functions are still in the same section as the hot one > depending on the linker. Ruijie has a patch to move all the cold functions > to a separate section, we a...

...ered volume, only first shard of new file goes on hot tier. https://bugzilla.redhat.com/show_bug.cgi?id=1549714 On sharded tiered volume, only first shard of new file goes on hot tier. On a sharded tiered volume, only the first shard of a new file goes on the hot tier, the rest are written to the cold tier. This is unfortunate for archival applications where the hot tier is fast, but the cold tier is very slow. After the tier- promote-frequency (default 120 seconds), all of the shards do migrate to hot tier, but for archival applications, this migration is not helpful since the file is likely t...

On Wed, 9 Sep 2020 at 19:26, Nemanja Ivanovic <nemanja.i.ibm at gmail.com> wrote: > - Default (i.e. no -profile-deopt-cold): do nothing > - Option with no arg (i.e. -profile-deopt-cold): add attribute only to > functions that have an execution count of zero > - Option with an arg (i.e. -profile-deopt-cold=<N>): add attribute to > functions that account for <N>% of total execution counts > I...

...rinceton.edu On Mon, Jun 1, 2020 at 11:28 AM Teresa Johnson <tejohnson at google.com> wrote: > > > On Sun, May 31, 2020 at 11:37 PM Ruijie Fang <ruijief at princeton.edu> > wrote: > >> Hello, >> I am Ruijie Fang, a GSoC student working on "Improve hot cold >> splitting to aggressively outline small blocks." Over the course of >> last week, I met with my mentor and co-mentor, Aditya Kumar, and >> Rodrigo Rocha, and we made a preliminary plan on improving the >> existing hot/cold splitting pass in LLVM through identifying p...

We would like to propose a new feature to disable optimizations on IR Functions that are considered “cold” by PGO profiles. The primary goal for this work is to improve code optimization speed (which also improves compilation and LTO speed) without making too much impact on target code performance. The mechanism is pretty simple: In the second phase (i.e. optimization phase) of PGO, we would add `optn...

...son at google.com> >> wrote: >> >>> >>> >>> On Sun, May 31, 2020 at 11:37 PM Ruijie Fang <ruijief at princeton.edu> >>> wrote: >>> >>>> Hello, >>>> I am Ruijie Fang, a GSoC student working on "Improve hot cold >>>> splitting to aggressively outline small blocks." Over the course of >>>> last week, I met with my mentor and co-mentor, Aditya Kumar, and >>>> Rodrigo Rocha, and we made a preliminary plan on improving the >>>> existing hot/cold splitting pa...

Hi Guys Got a quick question regarding hot tier and cold tier. I got a gluster volume with 1 x 3 hot tier and 1 x 3 cold tier. watermark-low is 75 and watermark-hi is 90. usage of volume is very less. My files always go to hot tier and cold tier at same time As I understand, data should go to hot tier only until demoted. Could someone please shed some li...

...rter than that now, but this description is good enough for the problem at hand). We're under pretty severe icache/iTLB pressure, so we do whatever we can to keep the hot path as compact as possible. One of the ways we do this is by dividing our code cache into three fixed-size areas: main, cold, and frozen. Our current, non-llvm codegen backend has one area tag per basic block, and most tracelets we compile will span all three areas. This means that if we emit code for tracelets A and then B, A's main code will be followed immediately by B's main code (and the same for cold/f...

....) A reboot helped though, but still... :) [this is the normal CentOS4 i686 SMP kernel 2.6.9-5.0.5.ELsmp] May 31 22:31:25 tcs kernel: oom-killer: gfp_mask=0xd0 May 31 22:31:25 tcs kernel: DMA per-cpu: May 31 22:31:25 tcs kernel: cpu 0 hot: low 2, high 6, batch 1 May 31 22:31:25 tcs kernel: cpu 0 cold: low 0, high 2, batch 1 May 31 22:31:25 tcs kernel: cpu 1 hot: low 2, high 6, batch 1 May 31 22:31:25 tcs kernel: cpu 1 cold: low 0, high 2, batch 1 May 31 22:31:25 tcs kernel: cpu 2 hot: low 2, high 6, batch 1 May 31 22:31:25 tcs kernel: cpu 2 cold: low 0, high 2, batch 1 May 31 22:31:25 tcs kerne...

Hi, The actual data will be in the hot tier only till demotion. The file that you see on the cold tier is just a linkto file of the file on the hot tier. These linkto file are necessary for the internal working of the tier. On Mon, Mar 5, 2018 at 1:16 PM, Sherin George <allmyforums at outlook.in> wrote: > Hi Guys > > Got a quick question regarding hot tier and cold tier. > I...

...d BranchProbability information is only used when attempting to inline the early return code, and not used to determine whether to outline the slow code. ### Proposed changes In addition to looking for early returns, we should utilize profile information to outline blocks that are considered cold. If we can sufficiently reduce the size of the original function via this type of outlining, inlining should be able to inline the rest of the hot code. ## Details With the presence of profile information, we have a view of what code is infrequently executed and make better decisions on wha...

Hi David, So I've began doing some implementation on the outlining portion of the code. Currently, I got the partial inliner to outline cold regions (single entry, single exit) of the code, based solely on the existence of ProfileSummaryInfo (ie. profiling data). However, I have some concerns on how this will co-exist with the existing code that peels early returns. The control flow looks something like this: // New Code: find cold r...

Hi David, The only reason I can see to use the 'pattern matching' part as a fall-back is in case we cannot inline the (what I'm assuming would be) a much bigger hot-path-only cloned function for whatever reason. What I'm assuming here is that after cold-region outlining, we may still have a large portion of the original function body to attempt to inline, whereas the pattern matching method will only contain a few basic blocks, giving a better chance to inline something. For your (2) point, I think we'll have to be careful here. Without a se...