On 11/28/2011 11:24 PM, Adam Litke wrote:
On Wed, Nov 23, 2011 at 10:41:32AM -0700, Eric Blake wrote:
Hmm - passing nparams==1 to set just read_bytes_sec has the side effect of wiping out any existing total_iops_sec, even though those two parameters seem somewhat orthogonal, all because we zero-initialized the struct that we pass on to the monitor command. Is that intended? I can live with it (but it probably ought to be documented), but we may want to consider being more flexible, by using '0' to clear a previous limit, but initializing to '-1' to imply the limit does not change. Then the qemu_monitor_json code should only emit the arguments that are actually being changed, rather than blindly always outputting 6 parameters even when the user only passed in one parameter. But I'm okay delaying that to a separate patch based on whether others think it would be a good improvement. +1. I believe I had pointed this out previously as well (albeit not as concisely as this).
Well, here is the description of block I/O throttling command 'block_io_set_throttle' in qmp-commands.hx. EQMP { .name = "block_set_io_throttle", .args_type = "device:B,bps:i?,bps_rd:i?,bps_wr:i?,iops:i?,iops_rd:i?,iops_wr:i?", .params = "device [bps] [bps_rd] [bps_wr] [iops] [iops_rd] [iops_wr]", .help = "change I/O throttle limits for a block drive", .user_print = monitor_user_noop, .mhandler.cmd_new = do_block_set_io_throttle, }, SQMP block_set_io_throttle ------------ Change I/O throttle limits for a block drive. Arguments: - "device": device name (json-string) - "bps": total throughput limit in bytes per second(json-int, optional) - "bps_rd": read throughput limit in bytes per second(json-int, optional) - "bps_wr": read throughput limit in bytes per second(json-int, optional) - "iops": total I/O operations per second(json-int, optional) - "iops_rd": read I/O operations per second(json-int, optional) - "iops_wr": write I/O operations per second(json-int, optional) Example: -> { "execute": "block_set_io_throttle", "arguments": { "device": "virtio0", "bps": "1000000", "bps_rd": "0", "bps_wr": "0", "iops": "0", "iops_rd": "0", "iops_wr": "0" } } <- { "return": {} } This qmp command need all these 6 parameters at one time in qemu, so zero-initialized the struct to meet If there is no setting value for some of the fields. -- Lei