Messages in this thread | | | From | Jeff Moyer <> | Subject | Re: [PATCH] blk: don't account discard request size | Date | Wed, 13 May 2015 09:10:25 -0400 |
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Shaohua Li <shli@fb.com> writes:
> In a workload with discard request, the IO throughput is generally much > higher than expected. This is quite confusing checking iostat. Discard > request doesn't really write data to drive, so don't account it. > > Signed-off-by: Shaohua Li <shli@fb.com> > --- > block/blk-core.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/block/blk-core.c b/block/blk-core.c > index fd154b9..0128d18 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -2138,7 +2138,11 @@ EXPORT_SYMBOL_GPL(blk_rq_err_bytes); > > void blk_account_io_completion(struct request *req, unsigned int bytes) > { > - if (blk_do_io_stat(req)) { > + /* > + * discard request doesn't really write @bytes to drive, > + * doesn't account it > + **/ > + if (blk_do_io_stat(req) && !(req->cmd_flags & REQ_DISCARD)) { > const int rw = rq_data_dir(req); > struct hd_struct *part; > int cpu;
I think you want to modify __get_request to not set REQ_IO_STAT for discard requests. This patch will still account the start of I/O, which means in_flight will be off.
Cheers, Jeff
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