From 7f609a1959b6489fdcbd26c3928611afcff4d134 Mon Sep 17 00:00:00 2001
From: Avi Kivity <avi@cloudius-systems.com>
Date: Sun, 24 Aug 2014 10:30:54 +0300
Subject: [PATCH] fileiotest: limit concurrency

Otherwise, all of the writes are submitted at once, consuming tons of memory,
and preventing reads from happening in parallel to writes.

Add a semaphore to limit the amount of parallel I/O.
---
 fileiotest.cc | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/fileiotest.cc b/fileiotest.cc
index 5f8c4fae77..e8ffc28773 100644
--- a/fileiotest.cc
+++ b/fileiotest.cc
@@ -9,26 +9,30 @@ struct file_test {
     file_test(file&& f) : f(std::move(f)) {}
     file f;
     semaphore sem = { 0 };
+    semaphore par = { 1000 };
 };
 
 int main(int ac, char** av) {
     static constexpr auto max = 10000;
     the_reactor.open_file_dma("testfile.tmp").then([] (file f) {
         auto ft = new file_test{std::move(f)};
-        for (size_t i = 0; i < 10000; ++i) {
-            auto wbuf = allocate_aligned_buffer<unsigned char>(4096, 4096);
-            std::fill(wbuf.get(), wbuf.get() + 4096, i);
-            auto wb = wbuf.get();
-            ft->f.dma_write(i * 4096, wb, 4096).then(
-                    [ft, i, wbuf = std::move(wbuf)] (size_t ret) mutable {
-                assert(ret == 4096);
-                auto rbuf = allocate_aligned_buffer<unsigned char>(4096, 4096);
-                auto rb = rbuf.get();
-                ft->f.dma_read(i * 4096, rb, 4096).then(
-                        [ft, i, rbuf = std::move(rbuf), wbuf = std::move(wbuf)] (size_t) mutable {
-                    bool eq = std::equal(rbuf.get(), rbuf.get() + 4096, wbuf.get());
-                    assert(eq);
-                    ft->sem.signal(1);
+        for (size_t i = 0; i < max; ++i) {
+            ft->par.wait().then([ft, i] {
+                auto wbuf = allocate_aligned_buffer<unsigned char>(4096, 4096);
+                std::fill(wbuf.get(), wbuf.get() + 4096, i);
+                auto wb = wbuf.get();
+                ft->f.dma_write(i * 4096, wb, 4096).then(
+                        [ft, i, wbuf = std::move(wbuf)] (size_t ret) mutable {
+                    assert(ret == 4096);
+                    auto rbuf = allocate_aligned_buffer<unsigned char>(4096, 4096);
+                    auto rb = rbuf.get();
+                    ft->f.dma_read(i * 4096, rb, 4096).then(
+                            [ft, i, rbuf = std::move(rbuf), wbuf = std::move(wbuf)] (size_t) mutable {
+                        bool eq = std::equal(rbuf.get(), rbuf.get() + 4096, wbuf.get());
+                        assert(eq);
+                        ft->sem.signal(1);
+                        ft->par.signal();
+                    });
                 });
             });
         }