um: UBD Improvements
UBD at present is extremely slow because it handles only
one request at a time in the IO thread and IRQ handler.
The single request at a time is replaced by handling multiple
requests as well as necessary workarounds for short reads/writes.
Resulting performance improvement in disk IO - 30%
Signed-off-by: Anton Ivanov <aivanov@kot-begemot.co.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>
diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index f354027..8541027 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -1,4 +1,5 @@
/*
+ * Copyright (C) 2015-2016 Anton Ivanov (aivanov@brocade.com)
* Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
* Licensed under the GPL
*/
@@ -58,6 +59,17 @@
int error;
};
+
+static struct io_thread_req * (*irq_req_buffer)[];
+static struct io_thread_req *irq_remainder;
+static int irq_remainder_size;
+
+static struct io_thread_req * (*io_req_buffer)[];
+static struct io_thread_req *io_remainder;
+static int io_remainder_size;
+
+
+
static inline int ubd_test_bit(__u64 bit, unsigned char *data)
{
__u64 n;
@@ -442,29 +454,91 @@
static int thread_fd = -1;
static LIST_HEAD(restart);
-/* XXX - move this inside ubd_intr. */
+/* Function to read several request pointers at a time
+* handling fractional reads if (and as) needed
+*/
+
+static int bulk_req_safe_read(
+ int fd,
+ struct io_thread_req * (*request_buffer)[],
+ struct io_thread_req **remainder,
+ int *remainder_size,
+ int max_recs
+ )
+{
+ int n = 0;
+ int res = 0;
+
+ if (*remainder_size > 0) {
+ memmove(
+ (char *) request_buffer,
+ (char *) remainder, *remainder_size
+ );
+ n = *remainder_size;
+ }
+
+ res = os_read_file(
+ fd,
+ ((char *) request_buffer) + *remainder_size,
+ sizeof(struct io_thread_req *)*max_recs
+ - *remainder_size
+ );
+ if (res > 0) {
+ n += res;
+ if ((n % sizeof(struct io_thread_req *)) > 0) {
+ /*
+ * Read somehow returned not a multiple of dword
+ * theoretically possible, but never observed in the
+ * wild, so read routine must be able to handle it
+ */
+ *remainder_size = n % sizeof(struct io_thread_req *);
+ WARN(*remainder_size > 0, "UBD IPC read returned a partial result");
+ memmove(
+ remainder,
+ ((char *) request_buffer) +
+ (n/sizeof(struct io_thread_req *))*sizeof(struct io_thread_req *),
+ *remainder_size
+ );
+ n = n - *remainder_size;
+ }
+ } else {
+ n = res;
+ }
+ return n;
+}
+
/* Called without dev->lock held, and only in interrupt context. */
static void ubd_handler(void)
{
- struct io_thread_req *req;
struct ubd *ubd;
struct list_head *list, *next_ele;
unsigned long flags;
int n;
+ int count;
while(1){
- n = os_read_file(thread_fd, &req,
- sizeof(struct io_thread_req *));
- if(n != sizeof(req)){
+ n = bulk_req_safe_read(
+ thread_fd,
+ irq_req_buffer,
+ &irq_remainder,
+ &irq_remainder_size,
+ UBD_REQ_BUFFER_SIZE
+ );
+ if (n < 0) {
if(n == -EAGAIN)
break;
printk(KERN_ERR "spurious interrupt in ubd_handler, "
"err = %d\n", -n);
return;
}
-
- blk_end_request(req->req, 0, req->length);
- kfree(req);
+ for (count = 0; count < n/sizeof(struct io_thread_req *); count++) {
+ blk_end_request(
+ (*irq_req_buffer)[count]->req,
+ 0,
+ (*irq_req_buffer)[count]->length
+ );
+ kfree((*irq_req_buffer)[count]);
+ }
}
reactivate_fd(thread_fd, UBD_IRQ);
@@ -1064,6 +1138,28 @@
if (register_blkdev(fake_major, "ubd"))
return -1;
}
+
+ irq_req_buffer = kmalloc(
+ sizeof(struct io_thread_req *) * UBD_REQ_BUFFER_SIZE,
+ GFP_KERNEL
+ );
+ irq_remainder = 0;
+
+ if (irq_req_buffer == NULL) {
+ printk(KERN_ERR "Failed to initialize ubd buffering\n");
+ return -1;
+ }
+ io_req_buffer = kmalloc(
+ sizeof(struct io_thread_req *) * UBD_REQ_BUFFER_SIZE,
+ GFP_KERNEL
+ );
+
+ io_remainder = 0;
+
+ if (io_req_buffer == NULL) {
+ printk(KERN_ERR "Failed to initialize ubd buffering\n");
+ return -1;
+ }
platform_driver_register(&ubd_driver);
mutex_lock(&ubd_lock);
for (i = 0; i < MAX_DEV; i++){
@@ -1458,31 +1554,51 @@
int io_thread(void *arg)
{
- struct io_thread_req *req;
- int n;
+ int n, count, written, res;
os_fix_helper_signals();
while(1){
- n = os_read_file(kernel_fd, &req,
- sizeof(struct io_thread_req *));
- if(n != sizeof(struct io_thread_req *)){
- if(n < 0)
+ n = bulk_req_safe_read(
+ kernel_fd,
+ io_req_buffer,
+ &io_remainder,
+ &io_remainder_size,
+ UBD_REQ_BUFFER_SIZE
+ );
+ if (n < 0) {
+ if (n == -EAGAIN) {
+ ubd_read_poll(-1);
+ continue;
+ } else {
printk("io_thread - read failed, fd = %d, "
- "err = %d\n", kernel_fd, -n);
- else {
- printk("io_thread - short read, fd = %d, "
- "length = %d\n", kernel_fd, n);
+ "err = %d,"
+ "reminder = %d\n",
+ kernel_fd, -n, io_remainder_size);
}
- continue;
}
- io_count++;
- do_io(req);
- n = os_write_file(kernel_fd, &req,
- sizeof(struct io_thread_req *));
- if(n != sizeof(struct io_thread_req *))
- printk("io_thread - write failed, fd = %d, err = %d\n",
- kernel_fd, -n);
+
+ for (count = 0; count < n/sizeof(struct io_thread_req *); count++) {
+ io_count++;
+ do_io((*io_req_buffer)[count]);
+ }
+
+ written = 0;
+
+ do {
+ res = os_write_file(kernel_fd, ((char *) io_req_buffer) + written, n);
+ if (res > 0) {
+ written += res;
+ } else {
+ if (res != -EAGAIN) {
+ printk("io_thread - read failed, fd = %d, "
+ "err = %d\n", kernel_fd, -n);
+ }
+ }
+ if (written < n) {
+ ubd_write_poll(-1);
+ }
+ } while (written < n);
}
return 0;