linux-kernel - Re: [PATCH v2] perf ordered_events: Optimise event object reuse

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Date:   Wed, 27 May 2020 12:25:33 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Matt Fleming <matt@...eblueprint.co.uk>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] perf ordered_events: Optimise event object reuse

On Tue, May 26, 2020 at 02:59:28PM +0100, Matt Fleming wrote:

SNIP

> +
> +/*
> + * Allocate a new event object from the free event cache.
> + *
> + * Find the first address range in the cache and carve out enough bytes
> + * for an ordered_event objects. The object with the lowest address is
> + * always returned so that subsequent allocations benefit from
> + * contiguous memory accesses (spatial locality).
> + */
> +static struct ordered_event *free_event_get_tree(struct ordered_events *oe)
> +{
> +	struct interval_tree_node *it;
> +	struct ordered_event *new;
> +	size_t bytes = sizeof(*new);
> +
> +	it = interval_tree_iter_first(&oe->cache.rb, 0, ULONG_MAX);
> +	if (!it)
> +		return NULL;
> +
> +	/* Has the cache memory been exhausted? */
> +	assert(cache_region_size(it) >= bytes);
> +
> +	new = (void *)it->start;
> +
> +	if (cache_region_size(it) == bytes) {
> +		interval_tree_remove(it, &oe->cache.rb);
> +		free(it);
> +	}
> +
> +	it->start += bytes;

this does not look right.. should this go to else path in above condition?

jirka

> +	return new;
> +}
> +

SNIP