Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34626
We need to check has_storage() before looking at it in
cloneSparseTensors(), to avoid gratuitously throwing.
Ideally, we'd add a test for this (I wrote one up but had to disable it),
but won't work until JIT Pickler supports sparse tensors.
ghstack-source-id: 100018077
Test Plan: buck test mode/dev-nosan caffe2/torch/fb/distributed/thriftRpcAgent/...
Differential Revision: D20399971
fbshipit-source-id: 5debfa8140eb1f949d37336330223962cc320abc
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31357
If a user selects a subset of a Tensor and sends it in an RPC, we were sending
the whole original Tensor Storage over the network.
While this sounds reasonable, in practice, we observed view-like Tensors being sent
over rpc, where only 1% of the data in the provided Tensor's Storage was
actually used/needed.
The simple solution here is to just force a clone in the serializer code if we see that
less than (arbitrary) half the bits are used, and the tensor is more than a nominal few KB.
Add related tests to ensure this doesn't break.
An alternate approach would be to modify the Pickler. That said, since Pickler is shared by more
components, the logic might be harder to tailor appropriately at that layer (particularly
given that the Pickler has explicit logic to share a single Storage* among several Tensors
that commonly point to the same Storage*).
It's possible that we might want to further refine the basic thresholds in this change.
In practice, we've seen a mostly bimodal distribution thus far for the percent of Tensor
Storage referred by a Tensor in observed rpcs (i.e. either 90%+ or sub-10% of the Storage
referenced), hence the existing 50% threshold here is probably not an unreasonable
starting point.
ghstack-source-id: 95925474
Test Plan: buck test mode/dev caffe2/test/cpp/rpc/...
Differential Revision: D19137056
fbshipit-source-id: e2b3a4dd0cc6e1de820fd0740aa1d59883dbf8d4
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29785
TLDR: This change improves process_group's serialization speed:
Serialize_Tensor64: 12.38us -> 1.99us (~-84%)
Deserialize_Tensor64: 33.89us -> 5.62us (~-84%)
Serialize_Tensor1M: 525.74us -> 285.43us (~-45%)
Deserialize_Tensor1M: 892.61us -> 273.68us (~-70%)
After speaking with the jit team, we had consensus that torch::save()/load()
are somewhat high-overhead for RPC serialization, mostly intended for
persistent disk data.
(Particularly, for large tensors, 35% of the time is spent in CRC checking, even
with the fb-side changes to subsitute 40x faster SSE-accelerated crc checking;
Also, for small tensors, the zip container overhead is considerable, as is the
overhead of lexing/parsing an embedded text python program for each RPC).
The jit team encouraged us to use jit::pickler, with the WriteableTensorData
way of outputting result tensors (not the default side-tensor table, or
with pickling the actual tensors). This ends up just pickling some tensor
metadata, and giving us some tensor blobs that we can mindlessly
blit over the wire (they copy to cpu memory if needed).
There is yet no standardized container format for the pickled data
(there is jit::pickle_save() checked in, but but it's experimental,
no load function is yet provided), but they encouraged us to just use
something sensible for this, and possibly revisit later. For now, I made
the directory headers slightly http-inspired.
Note that serialization is just one component of the pipeline, but that
said, we also see reasonable reductions in end-to-end echo times (noisier):
ProcessGroupAgent_Echo(Tensor_Small) 855.25us -> 492.65us (~-42%)
ProcessGroupAgent_Echo(Tensor_1M) 10.82ms -> 6.94ms (~-35%)
ProcessGroupAgent_Echo(Small_NoTensor) 688.82us -> 301.72us (~-56%)
ProcessGroupAgent_Echo(1MB_NoTensor) 4.65ms -> 3.71ms (~-20%)
I moved the "wire serialization" logic to a separate file to assist with
unittesting.
ghstack-source-id: 94694682
Test Plan:
buck test mode/dev-nosan caffe2/test/cpp/api:serialize
buck test mode/dev-nosan caffe2/test/...
Differential Revision: D18493938
fbshipit-source-id: 07ddfe87dbe56472bc944f7d070627052c94a8f4
