Messages in this thread | | | Date | Tue, 22 May 2012 23:14:55 +0800 | From | Tao Ma <> | Subject | Re: [RFC] block/throttle: Add IO throttled information in blkcg. |
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On 05/22/2012 11:06 PM, Vivek Goyal wrote: > On Tue, May 22, 2012 at 10:44:11PM +0800, Tao Ma wrote: >> Hi Vivek, >> Thanks for the quick response. >> On 05/22/2012 07:11 PM, Vivek Goyal wrote: >>> On Tue, May 22, 2012 at 04:10:36PM +0800, Tao Ma wrote: >>>> From: Tao Ma <boyu.mt@taobao.com> >>>> >>>> Currently, if the IO is throttled by io-throttle, the SA has no idea of >>>> the situation and can't report it to the real application user about >>>> that he/she has to do something. So this patch adds a new interface >>>> named blkio.throttle.io_throttled which indicates how many IOs are >>>> currently throttled. >>> >>> If the only purpose is to know whether IOs are being throttled, why >>> not just scan for the rules and see if respective device has any >>> throttling rules or not. >> Sorry, but setting a throttling rules doesn't mean the IOs are >> throttled, right? So scanning doesn't work here IMHO. > > It means IOs will be throttled if you cross a certain rate. But yes, it > does not give any information that if at time T if there are any bios > throttled in the queue or not. > >>> >>> Even if you introduce this interface, you will end up scanning for >>> throttled ios against that particular device. And if IO is not happening >>> at that moment or if IO rate is not exceeding the rate limit, there >>> might not be any throttled ios and one might get misled. >> Oh, no actually in a *clound computing* environment, it is really >> useful, not misled. So let me describe it in more detail. Our product >> system will limit every instance to an approximate number at first, and >> then watch out the IOs being throttled. If these numbers is high, it can: >> 1) Shout loudly to the application programmer about the abuse if he >> sends out too much IO requests. >> 2) If it is not too much and some other instances are not active, adjust >> the throttled ratio so that this instance can work much faster. > > Ok, so you want to use this more as "congestion" parameter which tells at > a given moment how busy the queue is, or in this instance how many IOs > are backlogged in a cgroup due to throttling limits. yeah, with this information the daemon can adjust these limits automatically. > > I guess, it is not a bad idea to export this stat then. Will > "blkio.throttle.queued" be a better name to reflect that how many bios > are currently queued in throttling layer of request queue. I have thought of this name at the very first time. But there is also another one named "blkio.queued" which indicated the IOs being queued in the scheduler. I don't want the user to be confused and that's the reason I use "blkio.throttle.io_throttled".
Thanks Tao
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