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Re: [Qemu-block] [PATCH RFC v3 3/8] block: add throttle block filter dri

From: Manos Pitsidianakis
Subject: Re: [Qemu-block] [PATCH RFC v3 3/8] block: add throttle block filter driver
Date: Wed, 28 Jun 2017 18:22:09 +0300
User-agent: NeoMutt/20170609-57-1e93be (1.8.3) 
On Wed, Jun 28, 2017 at 04:40:12PM +0200, Kevin Wolf wrote:

Am 23.06.2017 um 14:46 hat Manos Pitsidianakis geschrieben:

block/throttle.c uses existing I/O throttle infrastructure inside a
block filter driver. I/O operations are intercepted in the filter's
read/write coroutines, and referred to block/throttle-groups.c

The driver can be used with the command
-drive driver=throttle,file.filename=foo.qcow2,iops-total=...
The configuration flags and semantics are identical to the hardcoded
throttling ones.

Signed-off-by: Manos Pitsidianakis <address@hidden>
---
 block/Makefile.objs             |   1 +
 block/throttle.c                | 427 ++++++++++++++++++++++++++++++++++++++++
 include/qemu/throttle-options.h |  60 ++++--
 3 files changed, 469 insertions(+), 19 deletions(-)
 create mode 100644 block/throttle.c

diff --git a/block/Makefile.objs b/block/Makefile.objs
index ea955302c8..bb811a4d01 100644
--- a/block/Makefile.objs
+++ b/block/Makefile.objs
@@ -25,6 +25,7 @@ block-obj-y += accounting.o dirty-bitmap.o
 block-obj-y += write-threshold.o
 block-obj-y += backup.o
 block-obj-$(CONFIG_REPLICATION) += replication.o
+block-obj-y += throttle.o

 block-obj-y += crypto.o

diff --git a/block/throttle.c b/block/throttle.c
new file mode 100644
index 0000000000..0c17051161
--- /dev/null
+++ b/block/throttle.c
@@ -0,0 +1,427 @@
+/*
+ * QEMU block throttling filter driver infrastructure
+ *
+ * Copyright (c) 2017 Manos Pitsidianakis
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 or
+ * (at your option) version 3 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */


Please consider using the LGPL. We're still hoping to turn the block
layer into a library one day, and almost all code in it is licensed
liberally (MIT or LGPL).


+#include "qemu/osdep.h"
+#include "block/throttle-groups.h"
+#include "qemu/throttle-options.h"
+#include "qapi/error.h"
+
+
+static QemuOptsList throttle_opts = {
+    .name = "throttle",
+    .head = QTAILQ_HEAD_INITIALIZER(throttle_opts.head),
+    .desc = {
+        {
+            .name = QEMU_OPT_IOPS_TOTAL,
+            .type = QEMU_OPT_NUMBER,
+            .help = "limit total I/O operations per second",
+        },{
+            .name = QEMU_OPT_IOPS_READ,
+            .type = QEMU_OPT_NUMBER,
+            .help = "limit read operations per second",
+        },{
+            .name = QEMU_OPT_IOPS_WRITE,
+            .type = QEMU_OPT_NUMBER,
+            .help = "limit write operations per second",
+        },{
+            .name = QEMU_OPT_BPS_TOTAL,
+            .type = QEMU_OPT_NUMBER,
+            .help = "limit total bytes per second",
+        },{
+            .name = QEMU_OPT_BPS_READ,
+            .type = QEMU_OPT_NUMBER,
+            .help = "limit read bytes per second",
+        },{
+            .name = QEMU_OPT_BPS_WRITE,
+            .type = QEMU_OPT_NUMBER,
+            .help = "limit write bytes per second",
+        },{
+            .name = QEMU_OPT_IOPS_TOTAL_MAX,
+            .type = QEMU_OPT_NUMBER,
+            .help = "I/O operations burst",
+        },{
+            .name = QEMU_OPT_IOPS_READ_MAX,
+            .type = QEMU_OPT_NUMBER,
+            .help = "I/O operations read burst",
+        },{
+            .name = QEMU_OPT_IOPS_WRITE_MAX,
+            .type = QEMU_OPT_NUMBER,
+            .help = "I/O operations write burst",
+        },{
+            .name = QEMU_OPT_BPS_TOTAL_MAX,
+            .type = QEMU_OPT_NUMBER,
+            .help = "total bytes burst",
+        },{
+            .name = QEMU_OPT_BPS_READ_MAX,
+            .type = QEMU_OPT_NUMBER,
+            .help = "total bytes read burst",
+        },{
+            .name = QEMU_OPT_BPS_WRITE_MAX,
+            .type = QEMU_OPT_NUMBER,
+            .help = "total bytes write burst",
+        },{
+            .name = QEMU_OPT_IOPS_TOTAL_MAX_LENGTH,
+            .type = QEMU_OPT_NUMBER,
+            .help = "length of the iopstotalmax burst period, in seconds",
+        },{
+            .name = QEMU_OPT_IOPS_READ_MAX_LENGTH,
+            .type = QEMU_OPT_NUMBER,
+            .help = "length of the iopsreadmax burst period, in seconds",
+        },{
+            .name = QEMU_OPT_IOPS_WRITE_MAX_LENGTH,
+            .type = QEMU_OPT_NUMBER,
+            .help = "length of the iopswritemax burst period, in seconds",
+        },{
+            .name = QEMU_OPT_BPS_TOTAL_MAX_LENGTH,
+            .type = QEMU_OPT_NUMBER,
+            .help = "length of the bpstotalmax burst period, in seconds",
+        },{
+            .name = QEMU_OPT_BPS_READ_MAX_LENGTH,
+            .type = QEMU_OPT_NUMBER,
+            .help = "length of the bpsreadmax burst period, in seconds",
+        },{
+            .name = QEMU_OPT_BPS_WRITE_MAX_LENGTH,
+            .type = QEMU_OPT_NUMBER,
+            .help = "length of the bpswritemax burst period, in seconds",
+        },{
+            .name = QEMU_OPT_IOPS_SIZE,
+            .type = QEMU_OPT_NUMBER,
+            .help = "when limiting by iops max size of an I/O in bytes",
+        },
+        {
+            .name = QEMU_OPT_THROTTLE_GROUP_NAME,
+            .type = QEMU_OPT_STRING,
+            .help = "throttle group name",
+        },
+        { /* end of list */ }
+    },
+};
+
+/* Extract ThrottleConfig options. Assumes cfg is initialized and will be
+ * checked for validity.
+ */
+
+static void throttle_extract_options(QemuOpts *opts, ThrottleConfig *cfg)
+{
+    if (qemu_opt_get(opts, QEMU_OPT_BPS_TOTAL)) {
+        cfg->buckets[THROTTLE_BPS_TOTAL].avg =
+            qemu_opt_get_number(opts, QEMU_OPT_BPS_TOTAL, 0);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_BPS_READ)) {
+        cfg->buckets[THROTTLE_BPS_READ].avg  =
+            qemu_opt_get_number(opts, QEMU_OPT_BPS_READ, 0);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_BPS_WRITE)) {
+        cfg->buckets[THROTTLE_BPS_WRITE].avg =
+            qemu_opt_get_number(opts, QEMU_OPT_BPS_WRITE, 0);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_IOPS_TOTAL)) {
+        cfg->buckets[THROTTLE_OPS_TOTAL].avg =
+            qemu_opt_get_number(opts, QEMU_OPT_IOPS_TOTAL, 0);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_IOPS_READ)) {
+        cfg->buckets[THROTTLE_OPS_READ].avg =
+            qemu_opt_get_number(opts, QEMU_OPT_IOPS_READ, 0);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_IOPS_WRITE)) {
+        cfg->buckets[THROTTLE_OPS_WRITE].avg =
+            qemu_opt_get_number(opts, QEMU_OPT_IOPS_WRITE, 0);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_BPS_TOTAL_MAX)) {
+        cfg->buckets[THROTTLE_BPS_TOTAL].max =
+            qemu_opt_get_number(opts, QEMU_OPT_BPS_TOTAL_MAX, 0);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_BPS_READ_MAX)) {
+        cfg->buckets[THROTTLE_BPS_READ].max  =
+            qemu_opt_get_number(opts, QEMU_OPT_BPS_READ_MAX, 0);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_BPS_WRITE_MAX)) {
+        cfg->buckets[THROTTLE_BPS_WRITE].max =
+            qemu_opt_get_number(opts, QEMU_OPT_BPS_WRITE_MAX, 0);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_IOPS_TOTAL_MAX)) {
+        cfg->buckets[THROTTLE_OPS_TOTAL].max =
+            qemu_opt_get_number(opts, QEMU_OPT_IOPS_TOTAL_MAX, 0);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_IOPS_READ_MAX)) {
+        cfg->buckets[THROTTLE_OPS_READ].max =
+            qemu_opt_get_number(opts, QEMU_OPT_IOPS_READ_MAX, 0);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_IOPS_WRITE_MAX)) {
+        cfg->buckets[THROTTLE_OPS_WRITE].max =
+            qemu_opt_get_number(opts, QEMU_OPT_IOPS_WRITE_MAX, 0);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_BPS_TOTAL_MAX_LENGTH)) {
+        cfg->buckets[THROTTLE_BPS_TOTAL].burst_length =
+            qemu_opt_get_number(opts, QEMU_OPT_BPS_TOTAL_MAX_LENGTH, 1);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_BPS_READ_MAX_LENGTH)) {
+        cfg->buckets[THROTTLE_BPS_READ].burst_length  =
+            qemu_opt_get_number(opts, QEMU_OPT_BPS_READ_MAX_LENGTH, 1);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_BPS_WRITE_MAX_LENGTH)) {
+        cfg->buckets[THROTTLE_BPS_WRITE].burst_length =
+            qemu_opt_get_number(opts, QEMU_OPT_BPS_WRITE_MAX_LENGTH, 1);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_IOPS_TOTAL_MAX_LENGTH)) {
+        cfg->buckets[THROTTLE_OPS_TOTAL].burst_length =
+            qemu_opt_get_number(opts, QEMU_OPT_IOPS_TOTAL_MAX_LENGTH, 1);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_IOPS_READ_MAX_LENGTH)) {
+        cfg->buckets[THROTTLE_OPS_READ].burst_length =
+            qemu_opt_get_number(opts, QEMU_OPT_IOPS_READ_MAX_LENGTH, 1);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_IOPS_WRITE_MAX_LENGTH)) {
+        cfg->buckets[THROTTLE_OPS_WRITE].burst_length =
+            qemu_opt_get_number(opts, QEMU_OPT_IOPS_WRITE_MAX_LENGTH, 1);
+    }
+    if (qemu_opt_get(opts, QEMU_OPT_IOPS_SIZE)) {
+        cfg->op_size =
+            qemu_opt_get_number(opts, QEMU_OPT_IOPS_SIZE, 0);
+    }
+}
+
+static int throttle_configure_tgm(BlockDriverState *bs, ThrottleGroupMember 
*tgm,
+                                                    QDict *options, Error 
**errp)


Both lines exceed 80 characters. The indentation is off, too: QDict on
the second line should be aligned with BlockDriverState on the first
one.


+{
+    int ret = 0;
+    ThrottleState *ts;
+    ThrottleTimers *tt;
+    ThrottleConfig cfg;
+    QemuOpts *opts = NULL;
+    const char *group_name = NULL;
+    Error *local_err = NULL;
+
+    opts = qemu_opts_create(&throttle_opts, NULL, 0, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return -EINVAL;
+    }
+    qemu_opts_absorb_qdict(opts, options, &local_err);
+    if (local_err) {
+        goto err;
+    }
+
+    group_name = qemu_opt_get(opts, QEMU_OPT_THROTTLE_GROUP_NAME);
+    if (!group_name) {
+        group_name = bdrv_get_device_or_node_name(bs);


This is a legacy function, we should avoid adding new callers.

Worse yet, if the group isn't specified, we want to create a new
group internally just for this throttle node. But nothing stops the user
from creating a group that is named like the device or node name of
another throttle node, so we might end up attaching to an existing
throttle group instead!

I think throttle groups should be anonymous rather than having a default
name if they are created implicitly.
Since we're moving groups to QOM we will need ids for each group. Can objects be anonymous? 





+        if (!strlen(group_name)) {


More efficiently written as if (!*group_name), but it should go away
anyway when you address the above comment.


+            error_setg(&local_err,
+                       "A group name must be specified for this device.");


You can directly set errp and avoid the error_propagate() later.


+            goto err;
+        }
+    }
+
+    tgm->aio_context = bdrv_get_aio_context(bs);
+    /* Register membership to group with name group_name */
+    throttle_group_register_tgm(tgm, group_name);
+
+    ts = tgm->throttle_state;
+    /* Copy previous configuration */
+    throttle_get_config(ts, &cfg);
+
+    /* Change limits if user has specified them */
+    throttle_extract_options(opts, &cfg);
+    if (!throttle_is_valid(&cfg, &local_err)) {


Here errp can directly be used, too.

You only need the &local_err idiom if you want to check whether an error
was set (because the caller might pass errp == NULL and then you can't
tell whether an error occurred or not).


+        throttle_group_unregister_tgm(tgm);
+        goto err;
+    }
+    tt = &tgm->throttle_timers;
+    /* Update group configuration */
+    throttle_config(ts, tt, &cfg);
+
+    qemu_co_queue_init(&tgm->throttled_reqs[0]);
+    qemu_co_queue_init(&tgm->throttled_reqs[1]);
+
+    goto fin;


I prefer an explicit ret = 0 right here because ret tends to be used to
store the return value for all kinds of functions. In this specific
case, it's still 0 from the initialisation, but that's easy to break
accidentally in a future patch.


+
+err:
+    error_propagate(errp, local_err);
+    ret = -EINVAL;
+fin:
+    qemu_opts_del(opts);
+    return ret;
+}
+
+static int throttle_open(BlockDriverState *bs, QDict *options,
+                            int flags, Error **errp)
+{
+    ThrottleGroupMember *tgm = bs->opaque;
+    Error *local_err = NULL;
+
+    bs->open_flags = flags;
+    bs->file = bdrv_open_child(NULL, options, "file",
+                                    bs, &child_file, false, &local_err);
+
+    if (local_err) {


If you check bs->file == NULL instead, you can avoid local_err.


+        error_propagate(errp, local_err);
+        return -EINVAL;
+    }
+
+    qdict_flatten(options);


Why do you need this? options should already be flattened.


+    return throttle_configure_tgm(bs, tgm, options, errp);
+}
+
+static void throttle_close(BlockDriverState *bs)
+{
+    ThrottleGroupMember *tgm = bs->opaque;
+    bdrv_drained_begin(bs);
+    throttle_group_unregister_tgm(tgm);
+    bdrv_drained_end(bs);
+    return;


This is a useless return statement. I think I've seen compilers warn
about it (and we use -Werror, so this would be a build failure on them).

bdrv_drained_begin/end should be unnecessary in .bdrv_close
implementations, we always drain all requests before calling the
callback.


+}
+
+
+static int64_t throttle_getlength(BlockDriverState *bs)
+{
+    return bdrv_getlength(bs->file->bs);
+}
+
+
+static int coroutine_fn throttle_co_preadv(BlockDriverState *bs, uint64_t 
offset,


This line exceeds 80 characters.


+                                            uint64_t bytes, QEMUIOVector *qiov,
+                                            int flags)


Indentation is off by one.


+{
+
+    ThrottleGroupMember *tgm = bs->opaque;
+    throttle_group_co_io_limits_intercept(tgm, bytes, false);
+
+    return bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
+}
+
+static int coroutine_fn throttle_co_pwritev(BlockDriverState *bs, uint64_t 
offset,


Another long line.


+                                            uint64_t bytes, QEMUIOVector *qiov,
+                                            int flags)
+{
+    ThrottleGroupMember *tgm = bs->opaque;
+    throttle_group_co_io_limits_intercept(tgm, bytes, true);
+
+    return bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
+}


Kevin
Thanks a lot for the comments. (This was one of the first things I wrote, so this is why it is not very idiomatic)

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