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[PATCH 2/3] buffer: remove ioctl syscall in common paths


From: Eric Wong
Subject: [PATCH 2/3] buffer: remove ioctl syscall in common paths
Date: Sun, 6 Oct 2013 11:34:52 +0000

We do not need this for single sink situations (the common case)
at all.  We also do not need to check IO#nread for splice, either;
we can just do non-blocking I/O.  The only common path where we
might still need it is the non-splice case with multiple sinks.
---
 lib/dtas/buffer.rb            |  7 ++-----
 lib/dtas/buffer/read_write.rb | 13 +++++++++----
 lib/dtas/buffer/splice.rb     | 21 +++++++++++++--------
 test/test_buffer.rb           | 20 --------------------
 4 files changed, 24 insertions(+), 37 deletions(-)

diff --git a/lib/dtas/buffer.rb b/lib/dtas/buffer.rb
index c9f096c..c0ba6a6 100644
--- a/lib/dtas/buffer.rb
+++ b/lib/dtas/buffer.rb
@@ -47,16 +47,13 @@ class DTAS::Buffer # :nodoc:
   # - some type of StandardError
   # - nil
   def broadcast(targets)
-    bytes = inflight
-    return :wait_readable if 0 == bytes # spurious wakeup
-
     case targets.size
     when 0
       :ignore # this will pause decoders
     when 1
-      broadcast_one(targets, bytes)
+      broadcast_one(targets)
     else # infinity
-      broadcast_inf(targets, bytes)
+      broadcast_inf(targets)
     end
   end
 
diff --git a/lib/dtas/buffer/read_write.rb b/lib/dtas/buffer/read_write.rb
index 0044400..11d1a95 100644
--- a/lib/dtas/buffer/read_write.rb
+++ b/lib/dtas/buffer/read_write.rb
@@ -17,25 +17,30 @@ module DTAS::Buffer::ReadWrite # :nodoc:
   def discard(bytes)
     buf = _rbuf
     begin
-      @to_io.read(bytes, buf) or break # EOF
+      @to_io.readpartial(bytes, buf)
       bytes -= buf.bytesize
+    rescue EOFError
+      return
     end until bytes == 0
   end
 
   # always block when we have a single target
-  def broadcast_one(targets, bytes)
+  def broadcast_one(targets)
     buf = _rbuf
-    @to_io.read(bytes, buf)
+    @to_io.readpartial(MAX_AT_ONCE, buf)
     n = targets[0].write(buf) # IO#write has write-in-full behavior
     @bytes_xfer += n
     :wait_readable
+  rescue EOFError
+    nil
   rescue Errno::EPIPE, IOError => e
     __dst_error(targets[0], e)
     targets.clear
     nil # do not return error here, we already spewed an error message
   end
 
-  def broadcast_inf(targets, bytes)
+  def broadcast_inf(targets)
+    bytes = inflight
     nr_nb = targets.count { |sink| sink.nonblock? }
     if nr_nb == 0 || nr_nb == targets.size
       # if all targets are full, don't start until they're all writable
diff --git a/lib/dtas/buffer/splice.rb b/lib/dtas/buffer/splice.rb
index 18dfd82..90c2e47 100644
--- a/lib/dtas/buffer/splice.rb
+++ b/lib/dtas/buffer/splice.rb
@@ -8,6 +8,7 @@ require_relative '../pipe'
 
 module DTAS::Buffer::Splice # :nodoc:
   MAX_AT_ONCE = 4096 # page size in Linux
+  MAX_AT_ONCE_1 = 65536
   MAX_SIZE = File.read("/proc/sys/fs/pipe-max-size").to_i
   DEVNULL = File.open("/dev/null", "r+")
   F_MOVE = IO::Splice::F_MOVE
@@ -28,9 +29,9 @@ module DTAS::Buffer::Splice # :nodoc:
     IO.splice(@to_io, nil, DEVNULL, nil, bytes)
   end
 
-  def broadcast_one(targets, bytes)
+  def broadcast_one(targets)
     # single output is always non-blocking
-    s = IO.trysplice(@to_io, nil, targets[0], nil, bytes, F_MOVE)
+    s = IO.trysplice(@to_io, nil, targets[0], nil, MAX_AT_ONCE_1, F_MOVE)
     if Symbol === s
       targets # our one and only target blocked on write
     else
@@ -48,11 +49,14 @@ module DTAS::Buffer::Splice # :nodoc:
     most_teed = 0
     targets.delete_if do |dst|
       begin
-        t = dst.nonblock? ?
+        t = (dst.nonblock? || most_teed == 0) ?
             IO.trytee(@to_io, dst, chunk_size) :
             IO.tee(@to_io, dst, chunk_size, WAITALL)
         if Integer === t
-          most_teed = t if t > most_teed
+          if t > most_teed
+            chunk_size = t if most_teed == 0
+            most_teed = t
+          end
         else
           blocked << dst
         end
@@ -65,7 +69,7 @@ module DTAS::Buffer::Splice # :nodoc:
     most_teed
   end
 
-  def broadcast_inf(targets, bytes)
+  def broadcast_inf(targets)
     if targets.none? { |sink| sink.nonblock? }
       # if all targets are blocking, don't start until they're all writable
       r = IO.select(nil, targets, nil, 0) or return targets
@@ -80,9 +84,10 @@ module DTAS::Buffer::Splice # :nodoc:
     end
 
     # don't pin too much on one target
-    bytes = bytes > MAX_AT_ONCE ? MAX_AT_ONCE : bytes
-
+    bytes = MAX_AT_ONCE
     last = targets.pop # we splice to the last one, tee to the rest
+
+    # this may return zero if all targets were non-blocking
     most_teed = __broadcast_tee(blocked, targets, bytes)
 
     # don't splice more than the largest amount we successfully teed
@@ -90,7 +95,7 @@ module DTAS::Buffer::Splice # :nodoc:
 
     begin
       targets << last
-      if last.nonblock?
+      if last.nonblock? || most_teed == 0
         s = IO.trysplice(@to_io, nil, last, nil, bytes, F_MOVE)
         if Symbol === s
           blocked << last
diff --git a/test/test_buffer.rb b/test/test_buffer.rb
index d74cdce..13f4352 100644
--- a/test/test_buffer.rb
+++ b/test/test_buffer.rb
@@ -51,13 +51,9 @@ class TestBuffer < Testcase
   def test_broadcast_1
     buf = new_buffer
     r, w = IO.pipe
-    assert_equal :wait_readable, buf.broadcast([w])
-    assert_equal 0, buf.bytes_xfer
     buf.wr.write "HIHI"
     assert_equal :wait_readable, buf.broadcast([w])
     assert_equal 4, buf.bytes_xfer
-    assert_equal :wait_readable, buf.broadcast([w])
-    assert_equal 4, buf.bytes_xfer
     tmp = [w]
     r.close
     buf.wr.write "HIHI"
@@ -90,20 +86,6 @@ class TestBuffer < Testcase
     a[1].nonblock = false
     b[0].read(b[0].nread)
     b[1].write(max)
-    t = Thread.new do
-      sleep 0.005
-      [ a[0].read(max.size).size, b[0].read(max.size).size ]
-    end
-    assert_equal 5, buf.__broadcast_tee(blocked, [a[1], b[1]], 5)
-    assert_equal [a[1]], blocked
-    assert_equal [ max.size, max.size ], t.value
-    b[0].close
-    tmp = [a[1], b[1]]
-
-    newerr = tmperr { assert_equal 5, buf.__broadcast_tee(blocked, tmp, 5) }
-    assert_equal [a[1]], blocked
-    assert_match(%r{dropping}, newerr.string)
-    assert_equal [a[1]], tmp
   end
 
   def test_broadcast
@@ -115,8 +97,6 @@ class TestBuffer < Testcase
     assert_equal 5, buf.bytes_xfer
     assert_equal "HELLO", a[0].read(5)
     assert_equal "HELLO", b[0].read(5)
-    assert_equal :wait_readable, buf.broadcast([a[1], b[1]])
-    assert_equal 5, buf.bytes_xfer
 
     return unless b[1].respond_to?(:pipe_size)
 
-- 
1.8.4




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