Graphite is great, but unfortunately the web UI itself isn't instrumented. (Yo dawg, I heard you like graphite.) Enable the directives to log render and cache performance, then monitor this with collect's tail plugin so you can visualize graphite performance.

README.md

collectd_tail_graphite.conf

LoadPlugin tail

<Plugin tail>

    # cache performance
    <File "/opt/graphite/storage/log/webapp/cache.log">
        Instance "graphite_web"

        <Match>
            Regex "Request-Cache hit "
            DSType "CounterInc"
            Type "counter"
            Instance "request_cache_hit"
        </Match>
        <Match>
            Regex "Request-Cache miss "
            DSType "CounterInc"
            Type "counter"
            Instance "request_cache_miss"
        </Match>
        <Match>
            Regex "CarbonLink creating a new socket "
            DSType "CounterInc"
            Type "counter"
            Instance "socket_create_count"
        </Match>
        <Match>
            Regex "CarbonLink cache-query request "
            DSType "CounterInc"
            Type "counter"
            Instance "query_count"
        </Match>
        <Match>
            Regex "CarbonLink set-metadata request "
            DSType "CounterInc"
            Type "counter"
            Instance "set-metadata_count"
        </Match>
        <Match>
            Regex "Data-Cache hit "
            DSType "CounterInc"
            Type "counter"
            Instance "data_cache_hit"
        </Match>
        <Match>
            Regex "Data-Cache miss "
            DSType "CounterInc"
            Type "counter"
            Instance "data_cache_miss"
        </Match>
    </File>

    # rendering performance
    <File "/opt/graphite/storage/log/webapp/rendering.log">
        Instance "graphite_web"

        # PNG's
        <Match>
            Regex "Rendered PNG in ([0-9\.]+) seconds"
            DSType "CounterInc"
            Type "requests"
            Instance "render_png_count"
        </Match>
        <Match>
            Regex "Rendered PNG in ([0-9\.]+) seconds"
            DSType "GaugeMin"
            Type "response_time"
            Instance "render_png_time_min"
        </Match>
        <Match>
            Regex "Rendered PNG in ([0-9\.]+) seconds"
            DSType "GaugeMax"
            Type "response_time"
            Instance "render_png_time_max"
        </Match>
        <Match>
            Regex "Rendered PNG in ([0-9\.]+) seconds"
            DSType "GaugeAverage"
            Type "response_time"
            Instance "render_png_time_avg"
        </Match>

        # pickle (carbonlink)
        <Match>
            Regex "Total pickle rendering time ([0-9\.]+)"
            DSType "CounterInc"
            Type "counter"
            Instance "render_pickle_count"
        </Match>
        <Match>
            Regex "Total pickle rendering time ([0-9\.]+)"
            DSType "GaugeMin"
            Type "response_time"
            Instance "render_pickle_time_min"
        </Match>
        <Match>
            Regex "Total pickle rendering time ([0-9\.]+)"
            DSType "GaugeMax"
            Type "response_time"
            Instance "render_pickle_time_max"
        </Match>
        <Match>
            Regex "Total pickle rendering time ([0-9\.]+)"
            DSType "GaugeAverage"
            Type "response_time"
            Instance "render_pickle_time_avg"
        </Match>

        # rawData (json, csv, etc)
        <Match>
            Regex "Total rawData rendering time ([0-9\.]+)"
            DSType "CounterInc"
            Type "counter"
            Instance "render_rawdata_count"
        </Match>
        <Match>
            Regex "Total rawData rendering time ([0-9\.]+)"
            DSType "GaugeMin"
            Type "response_time"
            Instance "render_rawdata_time_min"
        </Match>
        <Match>
            Regex "Total rawData rendering time ([0-9\.]+)"
            DSType "GaugeMax"
            Type "response_time"
            Instance "render_rawdata_time_max"
        </Match>
        <Match>
            Regex "Total rawData rendering time ([0-9\.]+)"
            DSType "GaugeAverage"
            Type "response_time"
            Instance "render_rawdata_time_avg"
        </Match>

        # total render time
        <Match>
            Regex "Total rendering time ([0-9\.]+) seconds"
            DSType "CounterInc"
            Type "counter"
            Instance "total_render_count"
        </Match>
        <Match>
            Regex "Total rendering time ([0-9\.]+) seconds"
            DSType "GaugeMin"
            Type "response_time"
            Instance "total_render_time_min"
        </Match>
        <Match>
            Regex "Total rendering time ([0-9\.]+) seconds"
            DSType "GaugeMax"
            Type "response_time"
            Instance "total_render_time_max"
        </Match>
        <Match>
            Regex "Total rendering time ([0-9\.]+) seconds"
            DSType "GaugeAverage"
            Type "response_time"
            Instance "total_render_time_avg"
        </Match>

        # cached response time
        <Match>
            Regex "Returned cached response in ([0-9\.]+) seconds"
            DSType "CounterInc"
            Type "counter"
            Instance "cached_response_time_count"
        </Match>
        <Match>
            Regex "Returned cached response in ([0-9\.]+) seconds"
            DSType "GaugeMin"
            Type "response_time"
            Instance "cached_response_time_min"
        </Match>
        <Match>
            Regex "Returned cached response in ([0-9\.]+) seconds"
            DSType "GaugeMax"
            Type "response_time"
            Instance "cached_response_time_max"
        </Match>
        <Match>
            Regex "Returned cached response in ([0-9\.]+) seconds"
            DSType "GaugeAverage"
            Type "response_time"
            Instance "cached_response_time_avg"
        </Match>

        # data retrieval time
        <Match>
            Regex "Retrieval of [^ ]+ took ([0-9\.]+)"
            DSType "CounterInc"
            Type "counter"
            Instance "retrieval_count"
        </Match>
        <Match>
            Regex "Retrieval of [^ ]+ took ([0-9\.]+)"
            DSType "GaugeMin"
            Type "response_time"
            Instance "retrieval_time_min"
        </Match>
        <Match>
            Regex "Retrieval of [^ ]+ took ([0-9\.]+)"
            DSType "GaugeMax"
            Type "response_time"
            Instance "retrieval_time_max"
        </Match>
        <Match>
            Regex "Retrieval of [^ ]+ took ([0-9\.]+)"
            DSType "GaugeAverage"
            Type "response_time"
            Instance "retrieval_time_avg"
        </Match>
    </File>

</Plugin>

Note that rawData (L109) really is only format=raw, it has nothing to do with the other formats mentioned in the comment.