fix gpt2 train loss Nan problem by add a line __syncthreads in BlockR… #33659
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PR types
Bug fixes
PR changes
OPs
Describe
背景：
gpt2 训练过程中出现loss不稳定、不收敛、最终变成nan的情况。
经排查：
1）在P40上训练正常，V100上训练出现异常。
2）添加一行log打印训练正常，无log打印训练异常。
3）使用原线性相加方式训练正常，使用BlockReduceSum训练异常。
最终添加一行__syncthreads后解决训练异常问题。
同时对另外两个BlockReduceSum做了同步修改。
对于shared[32]使用的共享内存大小数据32，来源是：
int wid = threadIdx.x / warpSize;
nvidia gpu blockdim最大1024，warpSize 32，所以改大小不超过maxblockdim/warpsize=32。
cherry-pick from:
#33658