From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7FBF33D6CAB for ; Tue, 24 Mar 2026 13:42:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774359748; cv=none; b=ncyjotrVmyNtSPqMhatnXRbmAgIVHngQjekgHo4VVWr7cWjl2T5BildeVba3xibXQNzI0vavlAwOQWOdK1YAz+TId8BiKsD/PQ+yJ4lWqbGJaBzdIcnlCWX10DVq+Wjd7ojkfRnnNNe9WONH+KNJd+4ztuRifzQETPf57ipdb1c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774359748; c=relaxed/simple; bh=1hd/g8rlYkxdHIVU0+5IZQ7zszyvb+TSb11ohVAJ62g=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=fqq0zG02yvj5oFtbYwgL/3Tpmhq0gDTgfzxIKmb4N7S7u0ToD2r2OtQ+ZK5xUqTfuBTYooJKY5FeqPiHBiHEKpGdwZ1FN35YNubfdXHipqx5lvFxGhW5YT28NKi8OSjnMq4eGNM1uYs0Ym4m3+O9mnDGWdCdqFeTzZUcEN0LsGQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=qKaJC+Dn; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="qKaJC+Dn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5796AC19424; Tue, 24 Mar 2026 13:42:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774359748; bh=1hd/g8rlYkxdHIVU0+5IZQ7zszyvb+TSb11ohVAJ62g=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=qKaJC+DnzMWKePMjYOU3AUHvk6bZBYjXum6NAY5evV7uY0Yxo1mvR2lEnAtn24UgH SLUvByjfBvypJ8GeGBHHTyjYW2wURRir/N51LQ8LRTGnhKb2MheuujYi9snAvs/1JL XvsygElETBt9T0GKHqqaao1vU0JNkqlGSjvMMvv/bTE9fx8S+W/3bkcMFuyYxrZkUR wWdyS0CB2HFQD36wMlMFyOdZHb8dkW/Mdr74dLGc/fUh10r4cK8GytcoUtbcSThtD3 bdKlQtu3c04SG3pJ7fTmch5CuBduR8fd3uEJyOmEyu3kPSXFzaHHCW12zT54Uqgmby 6JLQSpjNjEPXw== Message-ID: <294ffcf440317af6cc6198196e7687fe0af66c14.camel@kernel.org> Subject: Re: [PATCH 3/3] sunrpc: skip svc_xprt_enqueue when transport is busy From: Jeff Layton To: Chuck Lever , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey Cc: linux-nfs@vger.kernel.org, Chuck Lever Date: Tue, 24 Mar 2026 09:42:25 -0400 In-Reply-To: <20260324130449.16437-4-cel@kernel.org> References: <20260324130449.16437-1-cel@kernel.org> <20260324130449.16437-4-cel@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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svc_xprt_resource_released() calls svc_xprt_enqueue() > whenever XPT_DATA or XPT_DEFERRED is set. During RPC > processing, svc_reserve_auth() reduces the reservation > counter and triggers this path while the current thread > still holds XPT_BUSY. The enqueue enters svc_xprt_ready(), > executes an smp_rmb(), READ_ONCE(), and tracepoint, then > returns false on seeing XPT_BUSY. >=20 > Trace data from a 256KB NFSv3 WRITE workload over TCP > shows this pattern generates roughly 195,000 wasted > enqueue calls -- approximately one per RPC -- each > paying the full svc_xprt_ready() cost for no benefit. >=20 > Add a BUSY check alongside the existing DATA|DEFERRED > check in svc_xprt_resource_released(). When the > transport is BUSY, the holder will call > svc_xprt_received() upon completion, which already > checks for pending work flags and re-enqueues. >=20 > Signed-off-by: Chuck Lever > --- > net/sunrpc/svc_xprt.c | 13 ++++++++++--- > 1 file changed, 10 insertions(+), 3 deletions(-) >=20 > diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c > index 36c8437cfd8d..d2b8f0396b6a 100644 > --- a/net/sunrpc/svc_xprt.c > +++ b/net/sunrpc/svc_xprt.c > @@ -440,16 +440,23 @@ static bool svc_xprt_reserve_slot(struct svc_rqst *= rqstp, struct svc_xprt *xprt) > /* > * After a caller releases write-space or a request slot, > * re-enqueue the transport only when there is pending > - * work that a thread could act on. The smp_mb() pairs > + * work that a thread could act on. The smp_mb() pairs > * with the smp_rmb() in svc_xprt_ready() and orders the > * preceding counter update before the flags read so a > * concurrent set_bit(XPT_DATA) is visible here. > + * > + * When the transport is BUSY, the thread holding it will > + * call svc_xprt_received() upon completion, which checks > + * for pending work and re-enqueues as needed. > */ > static void svc_xprt_resource_released(struct svc_xprt *xprt) > { > + unsigned long xpt_flags; > + > smp_mb(); > - if (READ_ONCE(xprt->xpt_flags) & > - (BIT(XPT_DATA) | BIT(XPT_DEFERRED))) > + xpt_flags =3D READ_ONCE(xprt->xpt_flags); > + if (xpt_flags & (BIT(XPT_DATA) | BIT(XPT_DEFERRED)) && > + !(xpt_flags & BIT(XPT_BUSY))) > svc_xprt_enqueue(xprt); > } > =20 Reviewed-by: Jeff Layton