rwbuffer: Optimize the buffer algorithm

avoid the buffer flush as much as possible

Change-Id: I902f374e9540b36bd0b0c77a34cab5014a2c24fc
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Signed-off-by: chao.an <anchao@xiaomi.com>

drivers/rwbuffer.c

@@ -136,7 +136,6 @@ static inline void rwb_resetwrbuffer(FAR struct rwbuffer_s *rwb)
 
   rwb->wrnblocks       = 0;
   rwb->wrblockstart    = (off_t)-1;
-  rwb->wrexpectedblock = (off_t)-1;
 }
 #endif
 
@@ -240,56 +239,160 @@ static ssize_t rwb_writebuffer(FAR struct rwbuffer_s *rwb,
                                off_t startblock, uint32_t nblocks,
                                FAR const uint8_t *wrbuffer)
 {
-  int ret;
+  uint32_t nwritten = nblocks;
 
   /* Write writebuffer Logic */
 
   rwb_wrcanceltimeout(rwb);
 
-  /* First: Should we flush out our cache? We would do that if (1) we already
+  /* Is data saved in the write buffer? */
-   * buffering blocks and the next block writing is not in the same sequence,
-   * or (2) the number of blocks would exceed our allocated buffer capacity
-   */
 
-  if (((startblock != rwb->wrexpectedblock) && (rwb->wrnblocks)) ||
+  if (rwb->wrnblocks > 0)
-      ((rwb->wrnblocks + nblocks) > rwb->wrmaxblocks))
     {
-      finfo("writebuffer miss, expected: %08x, given: %08x\n",
+      off_t wrbend;
-            rwb->wrexpectedblock, startblock);
+      off_t newend;
 
-      /* Flush the write buffer */
+      /* Now there are five cases:
+       *
+       * 1. We update the non-overlapping region
+       */
 
-      ret = rwb->wrflush(rwb->dev, rwb->wrbuffer, rwb->wrblockstart,
+      wrbend = rwb->wrblockstart + rwb->wrnblocks;
-                         rwb->wrnblocks);
+      newend = startblock + nblocks;
-      if (ret < 0)
+
+      if (wrbend < startblock || rwb->wrblockstart > newend)
         {
-          ferr("ERROR: Error writing multiple from cache: %d\n", -ret);
+          /* Nothing to do */;
-          return ret;
         }
 
-      rwb_resetwrbuffer(rwb);
+      /* 2. We update the entire write buffer. */
+
+      else if (rwb->wrblockstart > startblock && wrbend < newend)
+        {
+          rwb->wrnblocks = 0;
+        }
+
+      /* We are going to update a subset of the write buffer.  Three
+       * more cases to consider:
+       *
+       * 3. We update a portion in the middle of the write buffer
+       */
+
+      else if (rwb->wrblockstart <= startblock && wrbend >= newend)
+        {
+          FAR uint8_t *dest;
+          size_t offset;
+
+          /* Copy the data to the middle of write buffer */
+
+          offset = startblock - rwb->wrblockstart;
+          dest   = rwb->wrbuffer + offset * rwb->blocksize;
+          memcpy(dest, wrbuffer, nblocks * rwb->blocksize);
+
+          nblocks = 0;
+        }
+
+      /* 4. We upate a portion at the end of the write buffer */
+
+      else if (wrbend >= startblock && wrbend <= newend)
+        {
+          FAR uint8_t *dest;
+          size_t offset;
+          size_t ncopy;
+
+          /* Copy the data from the updating region to the end
+           * of the write buffer.
+           */
+
+          offset = rwb->wrnblocks - (wrbend - startblock);
+          ncopy  = rwb->wrmaxblocks - offset;
+          if (ncopy > nblocks)
+            {
+              ncopy = nblocks;
+            }
+
+          dest = rwb->wrbuffer + offset * rwb->blocksize;
+          memcpy(dest, wrbuffer, ncopy * rwb->blocksize);
+
+          rwb->wrnblocks = offset + ncopy;
+          wrbuffer      += ncopy * rwb->blocksize;
+          startblock    += ncopy;
+          nblocks       -= ncopy;
+        }
+
+      /* 5. We update a portion at the beginning of the write buffer */
+
+      else /* if (rwb->wrblockstart >= startblock && wrbend >= newend) */
+        {
+          FAR uint8_t *dest;
+          FAR const uint8_t *src;
+          size_t ncopy;
+
+          DEBUGASSERT(rwb->wrblockstart >= startblock && wrbend >= newend);
+
+          /* Move the cached data to the end of the write buffer */
+
+          ncopy = rwb->wrblockstart - startblock;
+          if (ncopy > rwb->wrmaxblocks - rwb->wrnblocks)
+            {
+              ncopy = rwb->wrmaxblocks - rwb->wrnblocks;
+            }
+
+          dest = rwb->wrbuffer + ncopy * rwb->blocksize;
+          memmove(dest, rwb->wrbuffer, ncopy * rwb->blocksize);
+
+          rwb->wrblockstart -= ncopy;
+          rwb->wrnblocks    += ncopy;
+
+          /* Copy the data from the updating region to the beginning
+           * of the write buffer.
+           */
+
+          ncopy = newend - rwb->wrblockstart;
+          src   = wrbuffer + (nblocks - ncopy) * rwb->blocksize;
+          memcpy(rwb->wrbuffer, src, ncopy * rwb->blocksize);
+
+          nblocks -= ncopy;
+        }
     }
 
-  /* writebuffer is empty? Then initialize it */
+  /* Use the block cache unless the buffer size is bigger than block cache */
 
-  if (rwb->wrnblocks == 0)
+  if (nblocks > rwb->wrmaxblocks)
     {
-      finfo("Fresh cache starting at block: 0x%08x\n", startblock);
+      ssize_t ret = rwb->wrflush(rwb->dev, wrbuffer, startblock, nblocks);
+      if (ret < 0)
+        {
+          return ret;
+        }
+    }
+  else if (nblocks)
+    {
+      /* Flush the write buffer */
+
+      if (rwb->wrnblocks > 0)
+        {
+          ssize_t ret = rwb->wrflush(rwb->dev, rwb->wrbuffer,
+                                     rwb->wrblockstart, rwb->wrnblocks);
+          if (ret < 0)
+            {
+              return ret;
+            }
+        }
+
+      /* Buffer the data in the write buffer */
+
+      memcpy(rwb->wrbuffer, wrbuffer, nblocks * rwb->blocksize);
       rwb->wrblockstart = startblock;
+      rwb->wrnblocks    = nblocks;
     }
 
-  /* Add data to cache */
+  if (rwb->wrnblocks > 0)
+    {
+      rwb_wrstarttimeout(rwb);
+    }
 
-  finfo("writebuffer: copying %d bytes from %p to %p\n",
+  return nwritten;
-        nblocks * rwb->blocksize, wrbuffer,
-        &rwb->wrbuffer[rwb->wrnblocks * rwb->blocksize]);
-  memcpy(&rwb->wrbuffer[rwb->wrnblocks * rwb->blocksize],
-         wrbuffer, nblocks * rwb->blocksize);
-
-  rwb->wrnblocks      += nblocks;
-  rwb->wrexpectedblock = rwb->wrblockstart + rwb->wrnblocks;
-  rwb_wrstarttimeout(rwb);
-  return nblocks;
 }
 #endif
 
@@ -454,7 +557,7 @@ int rwb_invalidate_writebuffer(FAR struct rwbuffer_s *rwb,
       /* We are going to invalidate a subset of the write buffer.  Three
        * more cases to consider:
        *
-       * 2. We invalidate a portion in the middle of the write buffer
+       * 3. We invalidate a portion in the middle of the write buffer
        */
 
       else if (rwb->wrblockstart < startblock && wrbend > invend)
@@ -488,7 +591,7 @@ int rwb_invalidate_writebuffer(FAR struct rwbuffer_s *rwb,
             }
         }
 
-      /* 3. We invalidate a portion at the end of the write buffer */
+      /* 4. We invalidate a portion at the end of the write buffer */
 
       else if (wrbend > startblock && wrbend <= invend)
         {
@@ -496,7 +599,7 @@ int rwb_invalidate_writebuffer(FAR struct rwbuffer_s *rwb,
           ret = OK;
         }
 
-      /* 4. We invalidate a portion at the beginning of the write buffer */
+      /* 5. We invalidate a portion at the beginning of the write buffer */
 
       else /* if (rwb->wrblockstart >= startblock && wrbend > invend) */
         {
@@ -1005,40 +1108,14 @@ ssize_t rwb_write(FAR struct rwbuffer_s *rwb, off_t startblock,
     {
       finfo("startblock=%d wrbuffer=%p\n", startblock, wrbuffer);
 
-      /* Use the block cache unless the buffer size is bigger than block
+      ret = nxsem_wait(&rwb->wrsem);
-       * cache.
+      if (ret < 0)
-       */
-
-      if (nblocks > rwb->wrmaxblocks)
         {
-          /* First flush the cache */
+          return (ssize_t)ret;
-
-          ret = nxsem_wait(&rwb->wrsem);
-          if (ret < 0)
-            {
-              return (ssize_t)ret;
-            }
-
-          rwb_wrflush(rwb);
-          rwb_semgive(&rwb->wrsem);
-
-          /* Then transfer the data directly to the media */
-
-          ret = rwb->wrflush(rwb->dev, wrbuffer, startblock, nblocks);
         }
-      else
-        {
-          /* Buffer the data in the write buffer */
 
-          ret = nxsem_wait(&rwb->wrsem);
+      ret = rwb_writebuffer(rwb, startblock, nblocks, wrbuffer);
-          if (ret < 0)
+      rwb_semgive(&rwb->wrsem);
-            {
-              return (ssize_t)ret;
-            }
-
-          ret = rwb_writebuffer(rwb, startblock, nblocks, wrbuffer);
-          rwb_semgive(&rwb->wrsem);
-        }
 
       /* On success, return the number of blocks that we were requested to
        * write.  This is for compatibility with the normal return of a block

include/nuttx/drivers/rwbuffer.h

@@ -144,7 +144,6 @@ struct rwbuffer_s
   uint8_t      *wrbuffer;        /* Allocated write buffer */
   uint16_t      wrnblocks;       /* Number of blocks in write buffer */
   off_t         wrblockstart;    /* First block in write buffer */
-  off_t         wrexpectedblock; /* Next block expected */
 #endif
 
   /* This is the state of the read-ahead buffering */