From 2420ad2f8f86494f9318ceaeea391502ee947095 Mon Sep 17 00:00:00 2001 From: David Gibson Date: Thu, 28 May 2026 15:02:12 +1000 Subject: tcp_splice: Remove questionable "optimisation" of pending bytes tracking We have a special path that avoids updating conn->pending when the amounts read and written are equal. This has a conceptual complexity cost, in particular, it means that conn->pending[] is not accurate to its normal meaning for a section of the loop body. conn->pending[] shares a cacheline with conn->pipe[] and conn->s[], so it's almost certainly cache-hot. It's questionable that avoiding the update of pending even outweighs the extra conditional branch, let alone saves anything of significance. Remove it. This allows us to move the updates to conn->pending closer to the actual splice() calls, making it easier to reason about its value. It also lets us move the conn->pending updates so they can piggy back on existing tests rather than needing a conditional expression to avoid clobbering it when splice() returns -1 (EAGAIN). Signed-off-by: David Gibson Signed-off-by: Stefano Brivio --- tcp_splice.c | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-) diff --git a/tcp_splice.c b/tcp_splice.c index 5f41258..565596d 100644 --- a/tcp_splice.c +++ b/tcp_splice.c @@ -500,6 +500,8 @@ static int tcp_splice_forward(struct ctx *c, if (!readlen) { conn_event(conn, FIN_RCVD(fromsidei)); } else if (readlen > 0) { + conn->pending[fromsidei] += readlen; + if (readlen >= (long)c->tcp.pipe_size * 90 / 100) more = SPLICE_F_MORE; @@ -524,16 +526,11 @@ static int tcp_splice_forward(struct ctx *c, flow_trace(conn, "%zi from write-side call (passed %zi)", written, c->tcp.pipe_size); - /* Most common case: skip updating count of pending bytes */ - if (readlen > 0 && readlen == written) - continue; - - conn->pending[fromsidei] += readlen > 0 ? readlen : 0; - conn->pending[fromsidei] -= written > 0 ? written : 0; - if (written < 0) break; + conn->pending[fromsidei] -= written; + if (conn->events & FIN_RCVD(fromsidei) && !conn->pending[fromsidei]) break; -- cgit v1.2.3