Matt Sinclair has submitted this change. (
https://gem5-review.googlesource.com/c/public/gem5/+/48340 )
Change subject: gpu-compute: Fix TLB coalescer starvation
......................................................................
gpu-compute: Fix TLB coalescer starvation
Currently, we are storing coalesced accesses in
an std::unordered_map indexed by a tick index, i.e.
issue tick / coalescing window. If there are
multiple coalesced requests, at different tick
indexes, to the same virtual address, then the
TLB coalescer will issue just the first one.
However, std::unordered_map is not a sorted
container and we issue coalesced requests by iterating
through such container. This means that the coalesced
request sent in TLBCoalescer::processProbeTLBEvent is
not necessarly the oldest one. Because of this, in
cases of high contention the oldest coalesced request
will have a huge TLB access latency.
To fix this issue, we will use an std::map which is
a sorted container and therefore guarantees the
oldest coalesced request will be sent first.
Change-Id: I9c7ab32c038d5e60f6b55236266a27b0cae8bfb0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/48340
Reviewed-by: Matt Sinclair <mattdsincl...@gmail.com>
Reviewed-by: Matthew Poremba <matthew.pore...@amd.com>
Maintainer: Matt Sinclair <mattdsincl...@gmail.com>
Tested-by: kokoro <noreply+kok...@google.com>
---
M src/gpu-compute/tlb_coalescer.hh
1 file changed, 1 insertion(+), 1 deletion(-)
Approvals:
Matthew Poremba: Looks good to me, approved
Matt Sinclair: Looks good to me, but someone else must approve; Looks
good to me, approved
kokoro: Regressions pass
diff --git a/src/gpu-compute/tlb_coalescer.hh
b/src/gpu-compute/tlb_coalescer.hh
index b97801b..fce8740 100644
--- a/src/gpu-compute/tlb_coalescer.hh
+++ b/src/gpu-compute/tlb_coalescer.hh
@@ -100,7 +100,7 @@
* option is to change it to curTick(), so we coalesce based
* on the receive time.
*/
- typedef std::unordered_map<int64_t, std::vector<coalescedReq>>
+ typedef std::map<int64_t, std::vector<coalescedReq>>
CoalescingFIFO;
CoalescingFIFO coalescerFIFO;
--
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Gerrit-Project: public/gem5
Gerrit-Branch: release-staging-v21-1
Gerrit-Change-Id: I9c7ab32c038d5e60f6b55236266a27b0cae8bfb0
Gerrit-Change-Number: 48340
Gerrit-PatchSet: 3
Gerrit-Owner: Kyle Roarty <kyleroarty1...@gmail.com>
Gerrit-Reviewer: Alex Dutu <alexandru.d...@amd.com>
Gerrit-Reviewer: Matt Sinclair <mattdsincl...@gmail.com>
Gerrit-Reviewer: Matthew Poremba <matthew.pore...@amd.com>
Gerrit-Reviewer: kokoro <noreply+kok...@google.com>
Gerrit-MessageType: merged
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