Messages in this thread | | | Date | Thu, 12 Apr 2001 12:22:52 -0400 (EDT) | From | Bart Trojanowski <> | Subject | Re: Asynchronous io |
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Hi CJ, you should really read the thread titled "Linux's implementation of poll() not scalable?" in the LKML archives, here is a link: http://www.uwsg.iu.edu/hypermail/linux/kernel/0010.3/0003.html There are many problems with the /dev/something interface for events and all is described in that thread.
I have worked on a way suggested by Linus to get rid of the hit in performance when using select() and poll(). I have a working model for TCP sockets (as that is what I wanted to speed up - a TCP based proxy). My implementation is still in alpha but is available here: http://www.jukie.net/~bart/kernel/fdevent/
Now, before anyone gets to excited... I spoke with Linus about this and he suggested that I speak with Ben LaHaise who is working on async io using some modifications to the wail queue. I have send him mail but have not heard from Ben - I guess he must be as busy as the rest of us with a full mailbox of messages that he has no time to reply to. :)
My implementation introduces two new system calls: bind_event and get_events (as descibed in Linus' email above). The project is still in an alpha stage so I don't have any benchmarks. I am working on this at my own time so progress is moving at a slow pace... unfortunately.
Regards, Bart.
On Thu, 12 Apr 2001, CJ wrote:
> //Linux really needs a clean basis for asynchronous and > //unbuffered i/o libraries. Something like the fork/thread > //clone(), but to replace select() and aio_* polling. This > //might be a start. And it is just a file and very like a > //pipe or socket. > > //Suppose we add /dev/qio with 64 byte sectors as follows: > > struct qio{ //64 byte i/o request > u16 flags; //0.0 request block variant, SEEK_SET... > u16 verb; //0.2 open,close,read,mmap,sync,write, > // ioctl > // mallocIO&read,write&freeIO, > // mallocIO,freeIO > // autothread might be an ioctl() > u16 errno; //0.4 per request status > u16 completehow; //0.6 queue,AST,pipe,SIGIO,SIGIO||delete ok > u64 offset; //1 > u32 length; //2.0 bytes requested > u32 timeout; //2.4 im ms or us? > u32 transferred; //3.0 bytes > u32 qiohandle; //3.4 for cancell or polling > void* handle; //4 (open & close might write) > void* buffer; //5 > void* callback; //6 optimize special cases w/ completehow > void* callparam; //7 > }; //all fields are read xor write > > //Writing to the device would schedule i/o, reading would reap > //completions. Bad writes would give the byte offset to the > //rejected sector field if detected synchronously. Multiple > //sector writes would be truncated on the first bad sector. > //Accepted writes would be buffered in the kernel. > > //Each open creates a new queue, each write is read in the > //same queue. Any number of threads can read or write a queue. > > //some cases might be simplified by kernel processed completions, > //such as VMS AST emulation, or putting results in a pipe. Hence > //completehow, which might use callback and callparam. > > //timeout? > //canceling i/o? > //Sun aio emulation? > //VMS qio emulation? > //MS IOCP emulation? > //malloc()&free() safe across threads? > //Should O_DIRECT would error unless properly aligned etc. > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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