io_uring: disable IORING_SETUP_DEFER_TASKRUN

Benefits unclear for now
Cloudef · Jun 21, 2024 · b51bcd2 · b51bcd2
1 parent 98a543e
commit b51bcd2
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Showing 3 changed files with 18 additions and 12 deletions.
diff --git a/examples/coro.zig b/examples/coro.zig
@@ -91,6 +91,8 @@ fn client() !void {
 }
 
 pub fn main() !void {
+    // var mem: [4096 * 1024]u8 = undefined;
+    // var fba = std.heap.FixedBufferAllocator.init(&mem);
     var gpa: std.heap.GeneralPurposeAllocator(.{}) = .{};
     defer _ = gpa.deinit();
     var scheduler = try coro.Scheduler.init(gpa.allocator(), .{});

diff --git a/flake.nix b/flake.nix
@@ -73,22 +73,22 @@
       ```
       % time     seconds  usecs/call     calls    errors syscall
       ------ ----------- ----------- --------- --------- ------------------
-       45.31    0.000087          14         6           io_uring_enter
-       24.48    0.000047          23         2           io_uring_setup
-        9.38    0.000018           4         4           mmap
-        6.77    0.000013           3         4           munmap
-        5.73    0.000011           5         2           close
-        2.60    0.000005           5         1           bind
-        2.08    0.000004           4         1           listen
-        1.56    0.000003           1         2           setsockopt
-        1.56    0.000003           3         1           io_uring_register
-        0.52    0.000001           1         1           gettid
+        0.00    0.000000           0         2           close
+        0.00    0.000000           0         4           mmap
+        0.00    0.000000           0         4           munmap
         0.00    0.000000           0         5           rt_sigaction
+        0.00    0.000000           0         1           bind
+        0.00    0.000000           0         1           listen
+        0.00    0.000000           0         2           setsockopt
         0.00    0.000000           0         1           execve
         0.00    0.000000           0         1           arch_prctl
+        0.00    0.000000           0         1           gettid
         0.00    0.000000           0         2           prlimit64
+        0.00    0.000000           0         2           io_uring_setup
+        0.00    0.000000           0         6           io_uring_enter
+        0.00    0.000000           0         1           io_uring_register
       ------ ----------- ----------- --------- --------- ------------------
-      100.00    0.000192           5        33           total
+      100.00    0.000000           0        33           total
       ```
       EOF
       '');

diff --git a/src/aio/IoUring.zig b/src/aio/IoUring.zig
@@ -170,7 +170,11 @@ inline fn uring_init_inner(n: u16, flags: u32) !std.os.linux.IoUring {
 
 inline fn uring_init(n: u16) aio.Error!std.os.linux.IoUring {
     const flags: []const u32 = &.{
-        std.os.linux.IORING_SETUP_SINGLE_ISSUER | std.os.linux.IORING_SETUP_DEFER_TASKRUN, // 6.1
+        // Disabled for now, this seems to increase syscalls a bit
+        // However, it may still be beneficial from latency perspective
+        // I need to play this with more later, and if there's no single answer
+        // then it might be better to be exposed as a tunable.
+        // std.os.linux.IORING_SETUP_SINGLE_ISSUER | std.os.linux.IORING_SETUP_DEFER_TASKRUN, // 6.1
         std.os.linux.IORING_SETUP_SINGLE_ISSUER | std.os.linux.IORING_SETUP_COOP_TASKRUN, // 6.0
         std.os.linux.IORING_SETUP_COOP_TASKRUN, // 5.9
         0, // 5.4