[PATCH 0/5] Add vhost-blk support

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Revision v1 of 3 in this series.

4 messages, 3 authors, 2012-07-16 · open the first message on its own page

[PATCH 0/5] Add vhost-blk support

From: Asias He <hidden>
Date: 2012-07-12 15:35:01

Hi folks,

This patchset adds vhost-blk support. vhost-blk is a in kernel virito-blk
device accelerator. Compared to userspace virtio-blk implementation, vhost-blk
gives about 5% to 15% performance improvement.

Asias He (5):
  aio: Export symbols and struct kiocb_batch for in kernel aio usage
  eventfd: Export symbol eventfd_file_create()
  vhost: Make vhost a separate module
  vhost-net: Use VHOST_NET_FEATURES for vhost-net
  vhost-blk: Add vhost-blk support

 drivers/vhost/Kconfig  |   20 +-
 drivers/vhost/Makefile |    6 +-
 drivers/vhost/blk.c    |  600 ++++++++++++++++++++++++++++++++++++++++++++++++
 drivers/vhost/net.c    |    4 +-
 drivers/vhost/test.c   |    4 +-
 drivers/vhost/vhost.c  |   48 ++++
 drivers/vhost/vhost.h  |   18 +-
 fs/aio.c               |   37 ++-
 fs/eventfd.c           |    1 +
 include/linux/aio.h    |   21 ++
 include/linux/vhost.h  |    1 +
 11 files changed, 729 insertions(+), 31 deletions(-)
 create mode 100644 drivers/vhost/blk.c

-- 
1.7.10.4

[PATCH 1/5] aio: Export symbols and struct kiocb_batch for in kernel aio usage

From: Asias He <hidden>
Date: 2012-07-12 15:35:02

This is useful for people who want to use aio in kernel, e.g. vhost-blk.

Signed-off-by: Asias He <redacted>
---
 fs/aio.c            |   37 ++++++++++++++++++-------------------
 include/linux/aio.h |   21 +++++++++++++++++++++
 2 files changed, 39 insertions(+), 19 deletions(-)
diff --git a/fs/aio.c b/fs/aio.c
index 55c4c76..93dfbdd 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -224,22 +224,24 @@ static void __put_ioctx(struct kioctx *ctx)
 	call_rcu(&ctx->rcu_head, ctx_rcu_free);
 }
 
-static inline int try_get_ioctx(struct kioctx *kioctx)
+inline int try_get_ioctx(struct kioctx *kioctx)
 {
 	return atomic_inc_not_zero(&kioctx->users);
 }
+EXPORT_SYMBOL(try_get_ioctx);
 
-static inline void put_ioctx(struct kioctx *kioctx)
+inline void put_ioctx(struct kioctx *kioctx)
 {
 	BUG_ON(atomic_read(&kioctx->users) <= 0);
 	if (unlikely(atomic_dec_and_test(&kioctx->users)))
 		__put_ioctx(kioctx);
 }
+EXPORT_SYMBOL(put_ioctx);
 
 /* ioctx_alloc
  *	Allocates and initializes an ioctx.  Returns an ERR_PTR if it failed.
  */
-static struct kioctx *ioctx_alloc(unsigned nr_events)
+struct kioctx *ioctx_alloc(unsigned nr_events)
 {
 	struct mm_struct *mm;
 	struct kioctx *ctx;
@@ -303,6 +305,7 @@ out_freectx:
 	dprintk("aio: error allocating ioctx %d\n", err);
 	return ERR_PTR(err);
 }
+EXPORT_SYMBOL(ioctx_alloc);
 
 /* kill_ctx
  *	Cancels all outstanding aio requests on an aio context.  Used 
@@ -436,23 +439,14 @@ static struct kiocb *__aio_get_req(struct kioctx *ctx)
 	return req;
 }
 
-/*
- * struct kiocb's are allocated in batches to reduce the number of
- * times the ctx lock is acquired and released.
- */
-#define KIOCB_BATCH_SIZE	32L
-struct kiocb_batch {
-	struct list_head head;
-	long count; /* number of requests left to allocate */
-};
-
-static void kiocb_batch_init(struct kiocb_batch *batch, long total)
+void kiocb_batch_init(struct kiocb_batch *batch, long total)
 {
 	INIT_LIST_HEAD(&batch->head);
 	batch->count = total;
 }
+EXPORT_SYMBOL(kiocb_batch_init);
 
-static void kiocb_batch_free(struct kioctx *ctx, struct kiocb_batch *batch)
+void kiocb_batch_free(struct kioctx *ctx, struct kiocb_batch *batch)
 {
 	struct kiocb *req, *n;
 
@@ -470,6 +464,7 @@ static void kiocb_batch_free(struct kioctx *ctx, struct kiocb_batch *batch)
 		wake_up_all(&ctx->wait);
 	spin_unlock_irq(&ctx->ctx_lock);
 }
+EXPORT_SYMBOL(kiocb_batch_free);
 
 /*
  * Allocate a batch of kiocbs.  This avoids taking and dropping the
@@ -540,7 +535,7 @@ out:
 	return allocated;
 }
 
-static inline struct kiocb *aio_get_req(struct kioctx *ctx,
+inline struct kiocb *aio_get_req(struct kioctx *ctx,
 					struct kiocb_batch *batch)
 {
 	struct kiocb *req;
@@ -552,6 +547,7 @@ static inline struct kiocb *aio_get_req(struct kioctx *ctx,
 	list_del(&req->ki_batch);
 	return req;
 }
+EXPORT_SYMBOL(aio_get_req);
 
 static inline void really_put_req(struct kioctx *ctx, struct kiocb *req)
 {
@@ -721,7 +717,7 @@ static inline int __queue_kicked_iocb(struct kiocb *iocb)
  * simplifies the coding of individual aio operations as
  * it avoids various potential races.
  */
-static ssize_t aio_run_iocb(struct kiocb *iocb)
+ssize_t aio_run_iocb(struct kiocb *iocb)
 {
 	struct kioctx	*ctx = iocb->ki_ctx;
 	ssize_t (*retry)(struct kiocb *);
@@ -815,6 +811,7 @@ out:
 	}
 	return ret;
 }
+EXPORT_SYMBOL(aio_run_iocb);
 
 /*
  * __aio_run_iocbs:
@@ -1136,7 +1133,7 @@ static inline void clear_timeout(struct aio_timeout *to)
 	del_singleshot_timer_sync(&to->timer);
 }
 
-static int read_events(struct kioctx *ctx,
+int read_events(struct kioctx *ctx,
 			long min_nr, long nr,
 			struct io_event __user *event,
 			struct timespec __user *timeout)
@@ -1252,6 +1249,7 @@ out:
 	destroy_timer_on_stack(&to.timer);
 	return i ? i : ret;
 }
+EXPORT_SYMBOL(read_events);
 
 /* Take an ioctx and remove it from the list of ioctx's.  Protects 
  * against races with itself via ->dead.
@@ -1492,7 +1490,7 @@ static ssize_t aio_setup_single_vector(int type, struct file * file, struct kioc
  *	Performs the initial checks and aio retry method
  *	setup for the kiocb at the time of io submission.
  */
-static ssize_t aio_setup_iocb(struct kiocb *kiocb, bool compat)
+ssize_t aio_setup_iocb(struct kiocb *kiocb, bool compat)
 {
 	struct file *file = kiocb->ki_filp;
 	ssize_t ret = 0;
@@ -1570,6 +1568,7 @@ static ssize_t aio_setup_iocb(struct kiocb *kiocb, bool compat)
 
 	return 0;
 }
+EXPORT_SYMBOL(aio_setup_iocb);
 
 static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
 			 struct iocb *iocb, struct kiocb_batch *batch,
diff --git a/include/linux/aio.h b/include/linux/aio.h
index b1a520e..4731da5 100644
--- a/include/linux/aio.h
+++ b/include/linux/aio.h
@@ -126,6 +126,16 @@ struct kiocb {
 	struct eventfd_ctx	*ki_eventfd;
 };
 
+/*
+ * struct kiocb's are allocated in batches to reduce the number of
+ * times the ctx lock is acquired and released.
+ */
+#define KIOCB_BATCH_SIZE	32L
+struct kiocb_batch {
+	struct list_head head;
+	long count; /* number of requests left to allocate */
+};
+
 #define is_sync_kiocb(iocb)	((iocb)->ki_key == KIOCB_SYNC_KEY)
 #define init_sync_kiocb(x, filp)			\
 	do {						\
@@ -216,6 +226,17 @@ struct mm_struct;
 extern void exit_aio(struct mm_struct *mm);
 extern long do_io_submit(aio_context_t ctx_id, long nr,
 			 struct iocb __user *__user *iocbpp, bool compat);
+extern struct kioctx *ioctx_alloc(unsigned nr_events);
+extern ssize_t aio_run_iocb(struct kiocb *iocb);
+extern int read_events(struct kioctx *ctx, long min_nr, long nr,
+		       struct io_event __user *event,
+		       struct timespec __user *timeout);
+extern ssize_t aio_setup_iocb(struct kiocb *kiocb, bool compat);
+extern void kiocb_batch_init(struct kiocb_batch *batch, long total);
+extern void kiocb_batch_free(struct kioctx *ctx, struct kiocb_batch *batch);
+extern struct kiocb *aio_get_req(struct kioctx *ctx, struct kiocb_batch *batch);
+extern int try_get_ioctx(struct kioctx *kioctx);
+extern void put_ioctx(struct kioctx *kioctx);
 #else
 static inline ssize_t wait_on_sync_kiocb(struct kiocb *iocb) { return 0; }
 static inline int aio_put_req(struct kiocb *iocb) { return 0; }
-- 
1.7.10.4

Re: [PATCH 0/5] Add vhost-blk support

From: Jeff Moyer <hidden>
Date: 2012-07-12 16:06:01

Asias He [off-list ref] writes:
Hi folks,

This patchset adds vhost-blk support. vhost-blk is a in kernel virito-blk
device accelerator. Compared to userspace virtio-blk implementation, vhost-blk
gives about 5% to 15% performance improvement.

Asias He (5):
  aio: Export symbols and struct kiocb_batch for in kernel aio usage
  eventfd: Export symbol eventfd_file_create()
  vhost: Make vhost a separate module
  vhost-net: Use VHOST_NET_FEATURES for vhost-net
  vhost-blk: Add vhost-blk support
I only saw patches 0 and 1.  Where are the other 4?  If the answer is,
"not on lkml," then please resend them, CC'ing lkml.  I'd like to be
able to see the usage of the aio routines.

Cheers,
Jeff

Re: [PATCH 0/5] Add vhost-blk support

From: Stefan Hajnoczi <hidden>
Date: 2012-07-16 11:58:21

On Thu, Jul 12, 2012 at 4:35 PM, Asias He [off-list ref] wrote:
This patchset adds vhost-blk support. vhost-blk is a in kernel virito-blk
device accelerator. Compared to userspace virtio-blk implementation, vhost-blk
gives about 5% to 15% performance improvement.
Why is it 5-15% faster?  vhost-blk and the userspace virtio-blk you
benchmarked should be doing basically the same thing:

1. An eventfd file descriptor is signalled when the vring has new
requests available from the guest.
2. A thread wakes up and processes the virtqueue.
3. Linux AIO is used to issue host I/O.
4. An interrupt is injected into the guest.

Does the vhost-blk implementation do anything fundamentally different
from userspace?  Where is the overhead that userspace virtio-blk has?

I'm asking because it would be beneficial to fix the overhead
(especially it that could speed up all userspace applications) instead
of adding a special-purpose kernel module to work around the overhead.

Stefan
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