> -----Original Message-----
> From: Jens Axboe <axboe@xxxxxxxxx>
> Sent: Friday, August 28, 2020 6:52 PM
> To: Elliott, Robert (Servers) <elliott@xxxxxxx>; Andreas Herrmann
> <aherrmann@xxxxxxxx>
> Subject: Re: [PATCH 1/2] thread_options: Add cgroup_use_bfq
>
...
> > ...
> >> @@ -593,11 +594,13 @@ struct thread_options_pack {
> >> uint8_t profile[FIO_TOP_STR_MAX];
> >>
> >> /*
> >> - * blkio cgroup support
> >> + * (blk)io cgroup support
> >> */
> >> uint8_t cgroup[FIO_TOP_STR_MAX];
> >> uint32_t cgroup_weight;
> >> uint32_t cgroup_nodelete;
> >> + uint32_t cgroup_use_bfq;
> >> + uint32_t padding; /* remove when possible to maintain
> alignment */
> >>
> >> uint32_t uid;
> >> uint32_t gid;
> >
> > Since the structure already has three pad fields:
> > uint32_t pad;
> >
> > uint64_t size;
> > ...
> > uint32_t pad2;
> > uint64_t rand_seed;
> > ...
> > uint32_t pad3;
> > fio_fp64_t percentile_list[FIO_IO_U_LIST_MAX_LEN];
> >
> > pad4 would seem like the natural name for another padding field,
> and
> > the comment doesn't seem necessary.
>
> Also worth checking if you can actually remove padding when updating
> it, rather than adding more.
I do think that one is needed, because there's a floating point
variable afterwards that libfio.c insists be aligned to an 8-byte
boundary.
The pahole utility reports the offsets (pre-patch) are:
/* --- cacheline 395 boundary (25280 bytes) was 24 bytes ago --- */
uint8_t cgroup[256]; /* 25304 256 */
/* --- cacheline 399 boundary (25536 bytes) was 24 bytes ago --- */
uint32_t cgroup_weight; /* 25560 4 */
uint32_t cgroup_nodelete; /* 25564 4 */
uint32_t uid; /* 25568 4 */
uint32_t gid; /* 25572 4 */
int32_t flow_id; /* 25576 4 */
int32_t flow; /* 25580 4 */
int32_t flow_watermark; /* 25584 4 */
uint32_t flow_sleep; /* 25588 4 */
uint64_t offset_increment; /* 25592 8 */
/* --- cacheline 400 boundary (25600 bytes) --- */
uint64_t number_ios; /* 25600 8 */
uint64_t latency_target; /* 25608 8 */
uint64_t latency_window; /* 25616 8 */
uint64_t max_latency; /* 25624 8 */
fio_fp64_t latency_percentile; /* 25632 16 */
libfio.c initialize_fio() excerpt:
/*
* We need these to be properly 64-bit aligned, otherwise we
* can run into problems on archs that fault on unaligned fp
* access (ARM).
*/
compiletime_assert((offsetof(struct thread_options_pack, zipf_theta) % 8) == 0, "zipf_theta");
compiletime_assert((offsetof(struct thread_options_pack, pareto_h) % 8) == 0, "pareto_h");
compiletime_assert((offsetof(struct thread_options_pack, percentile_list) % 8) == 0, "percentile_list");
compiletime_assert((offsetof(struct thread_options_pack, latency_percentile) % 8) == 0, "latency_percentile");
