Clarified use of Mebibytes and Gibibytes for sizes

AddyLaddy · AddyLaddy · commit 7278698c1bbd · 2026-01-06T14:59:17.000-08:00
diff --git a/README.md b/README.md
@@ -32,13 +32,14 @@ NCCL tests can run on multiple processes, multiple threads, and multiple CUDA de
 
 ### Quick examples
 
-Run on single node with 8 GPUs (`-g 8`), scanning from 8 Bytes to 128MBytes :
+Run on single node with 8 GPUs (`-g 8`), scanning from 8 Bytes to 128MiB (Mebibytes), doubling between each test (`-f 2`) :
 
 ```shell
 $ ./build/all_reduce_perf -b 8 -e 128M -f 2 -g 8
 ```
 
-Run 64 MPI processes on nodes with 8 GPUs each, for a total of 64 GPUs spread across 8 nodes :
+Run 64 MPI processes on nodes with 8 GPUs each, for a total of 64 GPUs spread across 8 nodes.
+Scanning from 8 Bytes to 32GiB (Gibibytes), doubling between each test (`-f 2`).
 (NB: The nccl-tests binaries must be compiled with `MPI=1` for this case)
 
 ```shell
@@ -57,10 +58,10 @@ All tests support the same set of arguments :
   * `-t,--nthreads <num threads>` number of threads per process. Default : 1.
   * `-g,--ngpus <GPUs per thread>` number of gpus per thread. Default : 1.
 * Sizes to scan
-  * `-b,--minbytes <min size in bytes>` minimum size to start with. Default : 32M.
-  * `-e,--maxbytes <max size in bytes>` maximum size to end at. Default : 32M.
-  * Increments can be either fixed or a multiplication factor. Only one of those should be used
-    * `-i,--stepbytes <increment size>` fixed increment between sizes. Default : 1M.
+  * `-b,--minbytes <min size in bytes>` minimum size to start with. Default : 32M (Mebibytes).
+  * `-e,--maxbytes <max size in bytes>` maximum size to end at. Default : 32M (Mebibytes).
+  * Increments can be either fixed or a multiplication factor. Only one of those should be used.
+    * `-i,--stepbytes <increment size>` fixed increment between sizes. Default : 1M (Mebibytes).
     * `-f,--stepfactor <increment factor>` multiplication factor between sizes. Default : disabled.
 * NCCL operations arguments
   * `-o,--op <sum/prod/min/max/avg/all>` Specify which reduction operation to perform. Only relevant for reduction operations like Allreduce, Reduce or ReduceScatter. Default : Sum.
diff --git a/src/common.cu b/src/common.cu
@@ -210,6 +210,7 @@ testResult_t initComms(ncclComm_t* comms, int nComms, int firstRank, int nRanks,
   return testSuccess;
 }
 
+// NOTE: We use the binary system, so M=Mebibytes and G=Gibibytes
 static double parsesize(const char *value) {
     long long int units;
     double size;

Original file line number	Diff line number	Diff line change
`@@ -210,6 +210,7 @@ testResult_t initComms(ncclComm_t* comms, int nComms, int firstRank, int nRanks,`
`210`	`210`	`return testSuccess;`
`211`	`211`	`}`
`212`	`212`
	`213`	`+// NOTE: We use the binary system, so M=Mebibytes and G=Gibibytes`
`213`	`214`	`static double parsesize(const char *value) {`
`214`	`215`	`long long int units;`
`215`	`216`	`double size;`