Re: [RFC PATCH 07/39] blktrace: add core trace API

From: Damien Le Moal <Damien.LeMoal@wdc.com>
To: Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>,
	"axboe@kernel.dk" <axboe@kernel.dk>,
	"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
	"rostedt@goodmis.org" <rostedt@goodmis.org>,
	"mingo@redhat.com" <mingo@redhat.com>,
	Johannes Thumshirn <Johannes.Thumshirn@wdc.com>,
	"bvanassche@acm.org" <bvanassche@acm.org>,
	"dongli.zhang@oracle.com" <dongli.zhang@oracle.com>,
	Aravind Ramesh <Aravind.Ramesh@wdc.com>,
	"joshi.k@samsung.com" <joshi.k@samsung.com>,
	Niklas Cassel <Niklas.Cassel@wdc.com>, "hch@lst.de" <hch@lst.de>,
	"osandov@fb.com" <osandov@fb.com>,
	"martin.petersen@oracle.com" <martin.petersen@oracle.com>
Cc: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [RFC PATCH 07/39] blktrace: add core trace API
Date: Fri, 26 Feb 2021 04:44:02 +0000	[thread overview]
Message-ID: <BL0PR04MB65140C6FFF7246AD07874152E79D9@BL0PR04MB6514.namprd04.prod.outlook.com> (raw)
In-Reply-To: 20210225070231.21136-8-chaitanya.kulkarni@wdc.com

On 2021/02/25 16:03, Chaitanya Kulkarni wrote:
> Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>

No commit message. Please add one.

> ---
>  kernel/trace/blktrace.c | 130 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 130 insertions(+)
> 
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index feb823b917ec..1aef55fdefa9 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -462,6 +462,136 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
>  	local_irq_restore(flags);
>  }
>  
> +/*
> + * Data direction bit lookup
> + */
> +static const u64 ddir_act_ext[2] = { BLK_TC_ACT_EXT(BLK_TC_READ),
> +				 BLK_TC_ACT_EXT(BLK_TC_WRITE) };
> +
> +/* The ilog2() calls fall out because they're constant */
> +#define MASK_TC_BIT_EXT(rw, __name) ((rw & REQ_ ## __name) << \
> +	  (ilog2(BLK_TC_ ## __name) + BLK_TC_SHIFT_EXT - __REQ_ ## __name))
> +
> +/*
> + * The worker for the various blk_add_trace*() types. Fills out a
> + * blk_io_trace structure and places it in a per-cpu subbuffer.
> + */

The comment is wrong. You are filling a blk_io_trace_ext structure. But I do not
see why that structure is needed in the first place. So the function below may
not be needed either. Modifying the existing one seems like a simpler approach
to me.

> +static void __blk_add_trace_ext(struct blk_trace_ext *bt, sector_t sector, int bytes,
> +		     int op, int op_flags, u64 what, int error, int pdu_len,
> +		     void *pdu_data, u64 cgid, u32 ioprio)
> +{
> +	struct task_struct *tsk = current;
> +	struct ring_buffer_event *event = NULL;
> +	struct trace_buffer *buffer = NULL;
> +	struct blk_io_trace_ext *t;
> +	unsigned long flags = 0;
> +	unsigned long *sequence;
> +	pid_t pid;
> +	int cpu, pc = 0;
> +	bool blk_tracer = blk_tracer_enabled;
> +	ssize_t cgid_len = cgid ? sizeof(cgid) : 0;
> +
> +	if (unlikely(bt->trace_state != Blktrace_running && !blk_tracer))
> +		return;
> +
> +	what |= ddir_act_ext[op_is_write(op) ? WRITE : READ];
> +	what |= MASK_TC_BIT_EXT(op_flags, SYNC);
> +	what |= MASK_TC_BIT_EXT(op_flags, RAHEAD);
> +	what |= MASK_TC_BIT_EXT(op_flags, META);
> +	what |= MASK_TC_BIT_EXT(op_flags, PREFLUSH);
> +	what |= MASK_TC_BIT_EXT(op_flags, FUA);
> +	if (op == REQ_OP_ZONE_APPEND)
> +		what |= BLK_TC_ACT_EXT(BLK_TC_ZONE_APPEND);
> +	if (op == REQ_OP_DISCARD || op == REQ_OP_SECURE_ERASE)
> +		what |= BLK_TC_ACT_EXT(BLK_TC_DISCARD);
> +	if (op == REQ_OP_FLUSH)
> +		what |= BLK_TC_ACT_EXT(BLK_TC_FLUSH);
> +	if (unlikely(op == REQ_OP_WRITE_ZEROES))
> +		what |= BLK_TC_ACT_EXT(BLK_TC_WRITE_ZEROES);
> +	if (unlikely(op == REQ_OP_ZONE_RESET))
> +		what |= BLK_TC_ACT_EXT(BLK_TC_ZONE_RESET);
> +	if (unlikely(op == REQ_OP_ZONE_RESET_ALL))
> +		what |= BLK_TC_ACT_EXT(BLK_TC_ZONE_RESET_ALL);
> +	if (unlikely(op == REQ_OP_ZONE_OPEN))
> +		what |= BLK_TC_ACT_EXT(BLK_TC_ZONE_OPEN);
> +	if (unlikely(op == REQ_OP_ZONE_CLOSE))
> +		what |= BLK_TC_ACT_EXT(BLK_TC_ZONE_CLOSE);
> +	if (unlikely(op == REQ_OP_ZONE_FINISH))
> +		what |= BLK_TC_ACT_EXT(BLK_TC_ZONE_FINISH);
> +
> +	if (cgid)
> +		what |= __BLK_TA_CGROUP;
> +
> +	pid = tsk->pid;
> +	if (act_log_check_ext(bt, what, sector, pid))
> +		return;
> +	if (bt->prio_mask && !prio_log_check(bt, ioprio))
> +		return;
> +
> +	cpu = raw_smp_processor_id();
> +
> +	if (blk_tracer) {
> +		tracing_record_cmdline(current);
> +
> +		buffer = blk_tr->array_buffer.buffer;
> +		pc = preempt_count();
> +		event = trace_buffer_lock_reserve(buffer, TRACE_BLK,
> +						  sizeof(*t) + pdu_len + cgid_len,
> +						  0, pc);
> +		if (!event)
> +			return;
> +		t = ring_buffer_event_data(event);
> +		goto record_it;
> +	}
> +
> +	if (unlikely(tsk->btrace_seq != blktrace_seq))
> +		trace_note_tsk_ext(tsk, ioprio);
> +
> +	/*
> +	 * A word about the locking here - we disable interrupts to reserve
> +	 * some space in the relay per-cpu buffer, to prevent an irq
> +	 * from coming in and stepping on our toes.
> +	 */
> +	local_irq_save(flags);
> +	t = relay_reserve(bt->rchan, sizeof(*t) + pdu_len + cgid_len);
> +	if (t) {
> +		sequence = per_cpu_ptr(bt->sequence, cpu);
> +
> +		t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION_EXT;
> +		t->sequence = ++(*sequence);
> +		t->time = ktime_to_ns(ktime_get());
> +record_it:
> +		/*
> +		 * These two are not needed in ftrace as they are in the
> +		 * generic trace_entry, filled by tracing_generic_entry_update,
> +		 * but for the trace_event->bin() synthesizer benefit we do it
> +		 * here too.
> +		 */
> +		t->cpu = cpu;
> +		t->pid = pid;
> +
> +		t->sector = sector;
> +		t->bytes = bytes;
> +		t->action = what;
> +		t->ioprio = ioprio;
> +		t->device = bt->dev;
> +		t->error = error;
> +		t->pdu_len = pdu_len + cgid_len;
> +
> +		if (cgid_len)
> +			memcpy((void *)t + sizeof(*t), &cgid, cgid_len);
> +		if (pdu_len)
> +			memcpy((void *)t + sizeof(*t) + cgid_len, pdu_data, pdu_len);
> +
> +		if (blk_tracer) {
> +			trace_buffer_unlock_commit(blk_tr, buffer, event, 0, pc);
> +			return;
> +		}
> +	}
> +
> +	local_irq_restore(flags);
> +}
> +
>  static void blk_trace_free(struct blk_trace *bt)
>  {
>  	relay_close(bt->rchan);
> 

-- 
Damien Le Moal
Western Digital Research