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SubjectRe: [RFC PATCH 4/6] relay: add relay_reserve_cpu()
* Tom Zanussi (zanussi@us.ibm.com) wrote:
> This patch adds the ability to explicitly specify the per-cpu buffer
> to reserve space in. Needed for early DTI tracing.
>

This should come with the ability to tell relay where the already
allocated static buffers are. Can you tell me a little more on why the
standard relay_reserve would not do the job? Is smp_processor_id() not
ready to output a sensible CPU id yet ?

> Signed-off-by: Tom Zanussi <zanussi@us.ibm.com>
> Signed-off-by: David Wilder <dwilder@us.ibm.com>
> ---
> relay.h | 33 +++++++++++++++++++++++++++++++++
> 1 file changed, 33 insertions(+)
>
> diff --git a/include/linux/relay.h b/include/linux/relay.h
> index 6caedef..37a7306 100644
> --- a/include/linux/relay.h
> +++ b/include/linux/relay.h
> @@ -269,6 +269,39 @@ static inline void *relay_reserve(struct rchan *chan, size_t length)
> }
>
> /**
> + * relay_reserve_cpu - reserve slot in given cpu's channel buffer
> + * @chan: relay channel
> + * @length: number of bytes to reserve
> + * @cpu: cpu to log to
> + *
> + * Returns pointer to reserved slot, NULL if full.
> + *
> + * Reserves a slot in the given cpu's channel buffer.
> + * Does not protect the buffer at all - caller must provide
> + * appropriate synchronization.
> + *
> + * NOTE: this is almost certainly not the function you want -
> + * use relay_reserve() instead for normal logging. This version
> + * is specialized for things like early tracing.
> + */
> +static inline void *relay_reserve_cpu(struct rchan *chan, size_t length,
> + unsigned int cpu)
> +{
> + void *reserved;
> + struct rchan_buf *buf = chan->buf[cpu];
> +
> + if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
> + length = relay_switch_subbuf(buf, length);
> + if (!length)
> + return NULL;
> + }
> + reserved = buf->data + buf->offset;
> + buf->offset += length;
> +
> + return reserved;
> +}
> +
> +/**
> * subbuf_start_reserve - reserve bytes at the start of a sub-buffer
> * @buf: relay channel buffer
> * @length: number of bytes to reserve
>
>
>
> -
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--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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