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Cache mask instead of dereferencing mask pointer

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This commit is contained in:
Joran Dirk Greef 2020-09-21 11:07:00 +02:00
parent 843c104fc9
commit 575ed941d7
1 changed files with 10 additions and 12 deletions
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22
lib/std/os/linux/io_uring.zig
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@ -108,7 +108,7 @@ pub const IO_Uring = struct {
// Check that our starting state is as we expect.
assert(sq.head.* == 0);
assert(sq.tail.* == 0);
assert(sq.mask.* == p.sq_entries - 1);
assert(sq.mask == p.sq_entries - 1);
// Allow flags.* to be non-zero, since the kernel may set IORING_SQ_NEED_WAKEUP at any time.
assert(sq.dropped.* == 0);
assert(sq.array.len == p.sq_entries);
@ -118,7 +118,7 @@ pub const IO_Uring = struct {
assert(cq.head.* == 0);
assert(cq.tail.* == 0);
assert(cq.mask.* == p.cq_entries - 1);
assert(cq.mask == p.cq_entries - 1);
assert(cq.overflow.* == 0);
assert(cq.cqes.len == p.cq_entries);
@ -152,7 +152,7 @@ pub const IO_Uring = struct {
// We must therefore use wrapping addition and subtraction to avoid a runtime crash.
const next = self.sq.sqe_tail +% 1;
if (next -% head > self.sq.sqes.len) return error.SubmissionQueueFull;
var sqe = &self.sq.sqes[self.sq.sqe_tail & self.sq.mask.*];
var sqe = &self.sq.sqes[self.sq.sqe_tail & self.sq.mask];
self.sq.sqe_tail = next;
// We zero the SQE slot here in a single place, rather than in many `queue_` methods.
@memset(@ptrCast([*]u8, sqe), 0, @sizeOf(io_uring_sqe));
@ -224,11 +224,10 @@ pub const IO_Uring = struct {
if (self.sq.sqe_head != self.sq.sqe_tail) {
// Fill in SQEs that we have queued up, adding them to the kernel ring.
const to_submit = self.sq.sqe_tail -% self.sq.sqe_head;
const mask = self.sq.mask.*;
var tail = self.sq.tail.*;
var i: usize = 0;
while (i < to_submit) : (i += 1) {
self.sq.array[tail & mask] = self.sq.sqe_head & mask;
self.sq.array[tail & self.sq.mask] = self.sq.sqe_head & self.sq.mask;
tail +%= 1;
self.sq.sqe_head +%= 1;
}
@ -292,14 +291,13 @@ pub const IO_Uring = struct {
fn copy_cqes_ready(self: *IO_Uring, cqes: []io_uring_cqe, wait_nr: u32) u32 {
const ready = self.cq_ready();
const count = std.math.min(cqes.len, ready);
const mask = self.cq.mask.*;
var head = self.cq.head.*;
var tail = head +% count;
// TODO Optimize this by using 1 or 2 memcpy's (if the tail wraps) rather than a loop.
var i: usize = 0;
// Do not use "less-than" operator since head and tail may wrap:
while (head != tail) {
cqes[i] = self.cq.cqes[head & mask]; // Copy struct by value.
cqes[i] = self.cq.cqes[head & self.cq.mask]; // Copy struct by value.
head +%= 1;
i += 1;
}
@ -560,7 +558,7 @@ pub const IO_Uring = struct {
pub const SubmissionQueue = struct {
head: *u32,
tail: *u32,
mask: *u32,
mask: u32,
flags: *u32,
dropped: *u32,
array: []u32,
@ -618,7 +616,7 @@ pub const SubmissionQueue = struct {
return SubmissionQueue {
.head = @ptrCast(*u32, @alignCast(@alignOf(u32), &mmap[p.sq_off.head])),
.tail = @ptrCast(*u32, @alignCast(@alignOf(u32), &mmap[p.sq_off.tail])),
.mask = @ptrCast(*u32, @alignCast(@alignOf(u32), &mmap[p.sq_off.ring_mask])),
.mask = @ptrCast(*u32, @alignCast(@alignOf(u32), &mmap[p.sq_off.ring_mask])).*,
.flags = @ptrCast(*u32, @alignCast(@alignOf(u32), &mmap[p.sq_off.flags])),
.dropped = @ptrCast(*u32, @alignCast(@alignOf(u32), &mmap[p.sq_off.dropped])),
.array = array[0..p.sq_entries],
@ -637,7 +635,7 @@ pub const SubmissionQueue = struct {
pub const CompletionQueue = struct {
head: *u32,
tail: *u32,
mask: *u32,
mask: u32,
overflow: *u32,
cqes: []io_uring_cqe,
@ -656,7 +654,7 @@ pub const CompletionQueue = struct {
return CompletionQueue {
.head = @ptrCast(*u32, @alignCast(@alignOf(u32), &mmap[p.cq_off.head])),
.tail = @ptrCast(*u32, @alignCast(@alignOf(u32), &mmap[p.cq_off.tail])),
.mask = @ptrCast(*u32, @alignCast(@alignOf(u32), &mmap[p.cq_off.ring_mask])),
.mask = @ptrCast(*u32, @alignCast(@alignOf(u32), &mmap[p.cq_off.ring_mask])).*,
.overflow = @ptrCast(*u32, @alignCast(@alignOf(u32), &mmap[p.cq_off.overflow])),
.cqes = cqes[0..p.cq_entries]
};
@ -670,7 +668,7 @@ pub const CompletionQueue = struct {
test "structs and offsets" {
if (builtin.os.tag != .linux) return error.SkipZigTest;
testing.expectEqual(@as(usize, 120), @sizeOf(io_uring_params));
testing.expectEqual(@as(usize, 64), @sizeOf(io_uring_sqe));
testing.expectEqual(@as(usize, 16), @sizeOf(io_uring_cqe));