improve cache line size (nim-lang#17885)

* improve cache line size

- 64bit system tend to use cache line of 64 bytes
- add align

https://trishagee.com/2011/07/22/dissecting_the_disruptor_why_its_so_fast_part_two__magic_cache_line_padding


Though I'm not sure, what do you think? @timotheecour

* Update lib/pure/concurrency/threadpool.nim

lib/pure/concurrency/threadpool.nim

@@ -52,17 +52,14 @@ proc signal(cv: var Semaphore) =
   release(cv.L)
   signal(cv.c)
 
-const CacheLineSize = 32 # true for most archs
+const CacheLineSize = 64 # true for most archs
 
 type
   Barrier {.compilerproc.} = object
     entered: int
     cv: Semaphore # Semaphore takes 3 words at least
-    when sizeof(int) < 8:
-      cacheAlign: array[CacheLineSize-4*sizeof(int), byte]
-    left: int
-    cacheAlign2: array[CacheLineSize-sizeof(int), byte]
-    interest: bool # whether the master is interested in the "all done" event
+    left {.align(CacheLineSize).}: int
+    interest {.align(CacheLineSize).} : bool # whether the master is interested in the "all done" event
 
 proc barrierEnter(b: ptr Barrier) {.compilerproc, inline.} =
   # due to the signaling between threads, it is ensured we are the only