From e352d56925111823395777d91bf5683739438da5 Mon Sep 17 00:00:00 2001
From: Charles Kerr <charles@transmissionbt.com>
Date: Tue, 24 Jul 2007 18:59:37 +0000
Subject: [PATCH] fix the high CPU load during endgame.

---
 libtransmission/peer.c      | 69 ++++++++++++++++++++++++++-----------
 libtransmission/peerutils.h | 31 ++++++++---------
 2 files changed, 64 insertions(+), 36 deletions(-)

diff --git a/libtransmission/peer.c b/libtransmission/peer.c
index 589bbf30d..4950b049a 100644
--- a/libtransmission/peer.c
+++ b/libtransmission/peer.c
@@ -645,34 +645,63 @@ writeEnd:
         && !peer->banned
         &&  peer->inRequestCount < peer->inRequestMax )
     {
-        int i;
         int poolSize = 0;
-        int * pool = getPreferredPieces ( tor, peer, &poolSize );
-        const int endgame = !poolSize;
+        int endgame = FALSE;
+        int openSlots = peer->inRequestMax - peer->inRequestCount;
+        int * pool = getPreferredPieces ( tor, peer, &poolSize, &endgame );
 
-        if( endgame ) /* endgame -- request everything we don't already have */
+        if( !endgame )
         {
-            for( i=0; i<tor->blockCount && peer->inRequestCount<peer->inRequestMax; ++i )
+            /* pool is sorted from most to least desirable pieces,
+               so work our way through starting at beginning */
+            int p;
+            for( p=0; p<poolSize && openSlots>0; )
             {
-                if( !isBlockInteresting( tor, peer, i ) )
-                    continue;
-                if( tr_bitfieldHas( peer->reqfield, i ) ) /* we've already asked them for it */
-                    continue;
-                if( !peer->reqfield )
-                    peer->reqfield = tr_bitfieldNew( tor->blockCount );
-                tr_bitfieldAdd( peer->reqfield, i );
-                sendRequest( tor, peer, i );
+                const int piece = pool[p];
+                const int block = tr_cpMissingBlockInPiece ( tor->completion, piece );
+                if( block < 0 )
+                    ++p;
+                else { 
+                    sendRequest( tor, peer, block );
+                    --openSlots;
+                }
             }
         }
-        else for( i=0; i<poolSize && peer->inRequestCount<peer->inRequestMax;  )
+        else
         {
-            int unused;
-            const int piece = pool[i];
-            const int block = tr_cpMissingBlockInPiece ( tor->completion, piece );
+            /* During endgame we remove the constraint of not asking for
+               pieces we've already requested from a different peer.
+               So if we follow the non-endgame approach of walking through
+               [0..poolCount) we'll bog down asking all peers for 1, then
+               all peers for 2, and so on.  Randomize our starting point
+               into "pool" to reduce such overlap */
+            int piecesLeft = poolSize;
+            int p = tr_rand( poolSize );
+            for( ; openSlots>0 && piecesLeft>0; --piecesLeft, p=(p+1)%poolSize )
+            {
+                const int piece = pool[p]; 
+                const int firstBlock = tr_pieceStartBlock( piece );
+                const int n = tr_pieceCountBlocks( piece );
+                const int end = firstBlock + n;
+                int block;
+                for( block=firstBlock; block<end; ++block )
+                {
+                    /* don't ask for it if we've already got it */
+                    if( tr_cpBlockIsComplete( tor->completion, block ))
+                        continue;
 
-            if( block>=0 )
-                sendRequest( tor, peer, block );
-            else ++i;
+                    /* don't ask for it twice from the same peer */
+                    if( tr_bitfieldHas( peer->reqfield, block ) )
+                        continue;
+
+                    /* ask peer for the piece */
+                    if( !peer->reqfield )
+                         peer->reqfield = tr_bitfieldNew( tor->blockCount );
+                    tr_bitfieldAdd( peer->reqfield, block );
+                    sendRequest( tor, peer, block );
+                    --openSlots;
+                }
+            }
         }
 
         tr_free( pool );
diff --git a/libtransmission/peerutils.h b/libtransmission/peerutils.h
index 67f757f9e..90014c502 100644
--- a/libtransmission/peerutils.h
+++ b/libtransmission/peerutils.h
@@ -181,19 +181,6 @@ static int isPieceInteresting( const tr_torrent_t  * tor,
     return 1;
 }
 
-static int isBlockInteresting( const tr_torrent_t  * tor,
-                               const tr_peer_t     * peer,
-                               int                   block )
-{
-    if( tr_cpBlockIsComplete( tor->completion, block )) /* we already have it */
-        return 0;
-
-    if( !isPieceInteresting( tor, peer, tr_blockPiece( block ))) /* is piece interesting? */
-        return 0;
-
-    return 1;
-}
-
 /***********************************************************************
  * isInteresting
  ***********************************************************************
@@ -263,12 +250,14 @@ int comparePieces (const void * aIn, const void * bIn)
 
 static int* getPreferredPieces( const tr_torrent_t  * tor,
                                 const tr_peer_t     * peer,
-                                int                 * pieceCount )
+                                int                 * pieceCount,
+                                int                 * isEndgame )
 {
     const tr_info_t * inf = &tor->info;
 
     int i;
     int poolSize = 0;
+    int endgame = FALSE;
     int * pool = tr_new( int, inf->pieceCount );
 
     for( i=0; i<inf->pieceCount; ++i )
@@ -276,14 +265,23 @@ static int* getPreferredPieces( const tr_torrent_t  * tor,
             if( tr_cpMissingBlocksForPiece( tor->completion, i ) )
                 pool[poolSize++] = i;
 
+    if( !poolSize ) {
+        endgame = TRUE;
+        for( i=0; i<inf->pieceCount; ++i )
+            if( isPieceInteresting( tor, peer, i ) )
+                pool[poolSize++] = i;
+    }
+
 #if 0
 fprintf (stderr, "old pool: ");
 for (i=0; i<15 && i<poolSize; ++i ) fprintf (stderr, "%d, ", pool[i] );
 fprintf (stderr, "\n");
 #endif
 
-    /* sort the rest from most interesting to least */
-    if( poolSize > 1 )
+    /* sort the rest from most interesting to least...
+       but not in endgame, because it asks for pieces in a
+       scattershot manner anyway and doesn't need them sorted */
+    if( !endgame && ( poolSize > 1 ) )
     {
         PieceCompareData * p = tr_new( PieceCompareData, poolSize );
 
@@ -316,6 +314,7 @@ for (i=0; i<15 && i<poolSize; ++i ) fprintf (stderr, "%d, ", pool[i] );
 fprintf (stderr, "\n");
 #endif
 
+    *isEndgame = endgame;
     *pieceCount = poolSize;
     return pool;
 }