| 5ef86c38 | 25-Jun-2022 |
Yinan Xu <[email protected]> |
freelist: optimize timing of read and writing (#1593)
This commit optimizes the timing of freelist by changing the updating
function of headPtr and tailPtr.
We maintains an one-hot representatio
freelist: optimize timing of read and writing (#1593)
This commit optimizes the timing of freelist by changing the updating
function of headPtr and tailPtr.
We maintains an one-hot representation of headPtr and further uses it to
read the free registers from the list, which should be better than the
previous implementation where headPtr is used to indexed into the queue.
The update of tailPtr and the freelist is delayed by one cycle to
optimize the timing. Because freelist allocates new registers in the
next cycle iff there are more than RenameWidth free registers in this
cycle. The freed registers in this cycle will never be used in the next
cycle. Thus, we can delay the updating of queue data to the next cycle.
We also move the update of tailPtr to the next cycle, since PopCount
takes a long timing and we move the last adder to the next cycle. Now
the adder works parallely with PopCount. That is, the updating of
tailPtr is pipelined.
show more ...
|
| 5010f3fb | 22-Jun-2022 |
Yinan Xu <[email protected]> |
core: add buffers for function units across int/fp (#1590)
This commit adds a buffer after the function unit that operate across
the integer block and the floating-point block, such as f2i and i2f.
core: add buffers for function units across int/fp (#1590)
This commit adds a buffer after the function unit that operate across
the integer block and the floating-point block, such as f2i and i2f.
For example, previously the out.ready of f2i depends on whether
mul/div/csr/jump has a valid instruction out, since f2i has lower
priority than them. This ready back-propagates from the integer function
units to the floating-point function units, and finally to the
floating-point reservation stations (since f2i is fully pipelined).
We add a buffer after the function unit to break this ready
back-propagation. It incurs one more cycle of execution latency, but we
leave it not-fully-optimized for now.
Timing can be further optimized if we separates the int writeback and fp
writeback in function units. In the current version, the ready of f2i
affects the ready of f2f pipelines, which is unnecessary. This is the
future work.
show more ...
|