netdev - Re: [PATCH v2 bpf-next 6/7] bpf: add BPF ringbuf and perf buffer benchmarks

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Message-ID: <20200522012147.shnwybm5my7dgy4v@ast-mbp.dhcp.thefacebook.com>
Date:   Thu, 21 May 2020 18:21:47 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...com,
        daniel@...earbox.net, andrii.nakryiko@...il.com,
        kernel-team@...com, "Paul E . McKenney" <paulmck@...nel.org>,
        Jonathan Lemon <jonathan.lemon@...il.com>
Subject: Re: [PATCH v2 bpf-next 6/7] bpf: add BPF ringbuf and perf buffer
 benchmarks

On Sun, May 17, 2020 at 12:57:26PM -0700, Andrii Nakryiko wrote:
> +
> +static inline int roundup_len(__u32 len)
> +{
> +	/* clear out top 2 bits */
> +	len <<= 2;
> +	len >>= 2;
> +	/* add length prefix */
> +	len += RINGBUF_META_LEN;
> +	/* round up to 8 byte alignment */
> +	return (len + 7) / 8 * 8;
> +}

the same round_up again?

> +
> +static void ringbuf_custom_process_ring(struct ringbuf_custom *r)
> +{
> +	unsigned long cons_pos, prod_pos;
> +	int *len_ptr, len;
> +	bool got_new_data;
> +
> +	cons_pos = smp_load_acquire(r->consumer_pos);
> +	while (true) {
> +		got_new_data = false;
> +		prod_pos = smp_load_acquire(r->producer_pos);
> +		while (cons_pos < prod_pos) {
> +			len_ptr = r->data + (cons_pos & r->mask);
> +			len = smp_load_acquire(len_ptr);
> +
> +			/* sample not committed yet, bail out for now */
> +			if (len & RINGBUF_BUSY_BIT)
> +				return;
> +
> +			got_new_data = true;
> +			cons_pos += roundup_len(len);
> +
> +			atomic_inc(&buf_hits.value);
> +		}
> +		if (got_new_data)
> +			smp_store_release(r->consumer_pos, cons_pos);
> +		else
> +			break;
> +	};
> +}

copy paste from libbpf? why?