Cache stream channel count in hot read/write path#68
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readStream() and writeStream() are the per-packet hot path. Each call
constructs a uhd::rx_streamer::buffs_type / tx_streamer::buffs_type
which needs the channel count:
uhd::rx_streamer::buffs_type stream_buffs(buffs, stream->get_num_channels());
^^^^^^^^^^^^^^^^^^^^^^^^
uhd::rx_streamer / tx_streamer are abstract base classes; get_num_channels
is a virtual call going through the vtable to the device-specific
streamer implementation. The channel count is established at
get_rx_stream() / get_tx_stream() time and never changes for the
lifetime of the streamer, so making the call once per readStream()
invocation is wasteful.
Cache it in SoapyUHDStream::num_channels at setupStream() time.
struct SoapyUHDStream
{
uhd::rx_streamer::sptr rx;
uhd::tx_streamer::sptr tx;
size_t num_channels = 0; // <-- new
};
Cost: one size_t per stream object. Benefit: one fewer indirect call
per packet on the read/write hot path, where SoapyUHD typically sees
hundreds to thousands of calls per second at high sample rates.
Build verified clean against UHD 4.10.0.0 (uhd-oc 4.10.0.0_1 keg).
No behavior change.
Signed-off-by: Tom Hensel <code@jitter.eu>
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Cache stream channel count in hot read/write path
Changed
get_num_channels()once atsetupStream()into a_nchanmember; use the cached value inreadStream()/writeStream().Why
get_num_channels()is virtual; called once perrecv/send. Caching skips the per-call dispatch in the hot path.