From c0f9c7e45d374ce6dc369443fa586c2fe228c345 Mon Sep 17 00:00:00 2001 From: Bert Kenward Date: Mon, 26 Oct 2015 14:23:42 +0000 Subject: [PATCH] sfc: replace spinlocks with bit ops for busy poll locking This patch reduces the overhead of locking for busy poll. Previously the state was protected by a lock, whereas now it's manipulated solely with atomic operations. Signed-off-by: Shradha Shah Signed-off-by: David S. Miller --- drivers/net/ethernet/sfc/efx.c | 4 +- drivers/net/ethernet/sfc/net_driver.h | 127 +++++++++++--------------- 2 files changed, 57 insertions(+), 74 deletions(-) diff --git a/drivers/net/ethernet/sfc/efx.c b/drivers/net/ethernet/sfc/efx.c index 974637d3ae25..6e11ee6173ce 100644 --- a/drivers/net/ethernet/sfc/efx.c +++ b/drivers/net/ethernet/sfc/efx.c @@ -2062,7 +2062,7 @@ static void efx_init_napi_channel(struct efx_channel *channel) netif_napi_add(channel->napi_dev, &channel->napi_str, efx_poll, napi_weight); napi_hash_add(&channel->napi_str); - efx_channel_init_lock(channel); + efx_channel_busy_poll_init(channel); } static void efx_init_napi(struct efx_nic *efx) @@ -2125,7 +2125,7 @@ static int efx_busy_poll(struct napi_struct *napi) if (!netif_running(efx->net_dev)) return LL_FLUSH_FAILED; - if (!efx_channel_lock_poll(channel)) + if (!efx_channel_try_lock_poll(channel)) return LL_FLUSH_BUSY; old_rx_packets = channel->rx_queue.rx_packets; diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h index ad56231743a6..229e68c89634 100644 --- a/drivers/net/ethernet/sfc/net_driver.h +++ b/drivers/net/ethernet/sfc/net_driver.h @@ -431,21 +431,8 @@ struct efx_channel { struct net_device *napi_dev; struct napi_struct napi_str; #ifdef CONFIG_NET_RX_BUSY_POLL - unsigned int state; - spinlock_t state_lock; -#define EFX_CHANNEL_STATE_IDLE 0 -#define EFX_CHANNEL_STATE_NAPI (1 << 0) /* NAPI owns this channel */ -#define EFX_CHANNEL_STATE_POLL (1 << 1) /* poll owns this channel */ -#define EFX_CHANNEL_STATE_DISABLED (1 << 2) /* channel is disabled */ -#define EFX_CHANNEL_STATE_NAPI_YIELD (1 << 3) /* NAPI yielded this channel */ -#define EFX_CHANNEL_STATE_POLL_YIELD (1 << 4) /* poll yielded this channel */ -#define EFX_CHANNEL_OWNED \ - (EFX_CHANNEL_STATE_NAPI | EFX_CHANNEL_STATE_POLL) -#define EFX_CHANNEL_LOCKED \ - (EFX_CHANNEL_OWNED | EFX_CHANNEL_STATE_DISABLED) -#define EFX_CHANNEL_USER_PEND \ - (EFX_CHANNEL_STATE_POLL | EFX_CHANNEL_STATE_POLL_YIELD) -#endif /* CONFIG_NET_RX_BUSY_POLL */ + unsigned long busy_poll_state; +#endif struct efx_special_buffer eventq; unsigned int eventq_mask; unsigned int eventq_read_ptr; @@ -480,98 +467,94 @@ struct efx_channel { }; #ifdef CONFIG_NET_RX_BUSY_POLL -static inline void efx_channel_init_lock(struct efx_channel *channel) +enum efx_channel_busy_poll_state { + EFX_CHANNEL_STATE_IDLE = 0, + EFX_CHANNEL_STATE_NAPI = BIT(0), + EFX_CHANNEL_STATE_NAPI_REQ_BIT = 1, + EFX_CHANNEL_STATE_NAPI_REQ = BIT(1), + EFX_CHANNEL_STATE_POLL_BIT = 2, + EFX_CHANNEL_STATE_POLL = BIT(2), + EFX_CHANNEL_STATE_DISABLE_BIT = 3, +}; + +static inline void efx_channel_busy_poll_init(struct efx_channel *channel) { - spin_lock_init(&channel->state_lock); + WRITE_ONCE(channel->busy_poll_state, EFX_CHANNEL_STATE_IDLE); } /* Called from the device poll routine to get ownership of a channel. */ static inline bool efx_channel_lock_napi(struct efx_channel *channel) { - bool rc = true; + unsigned long prev, old = READ_ONCE(channel->busy_poll_state); - spin_lock_bh(&channel->state_lock); - if (channel->state & EFX_CHANNEL_LOCKED) { - WARN_ON(channel->state & EFX_CHANNEL_STATE_NAPI); - channel->state |= EFX_CHANNEL_STATE_NAPI_YIELD; - rc = false; - } else { - /* we don't care if someone yielded */ - channel->state = EFX_CHANNEL_STATE_NAPI; + while (1) { + switch (old) { + case EFX_CHANNEL_STATE_POLL: + /* Ensure efx_channel_try_lock_poll() wont starve us */ + set_bit(EFX_CHANNEL_STATE_NAPI_REQ_BIT, + &channel->busy_poll_state); + /* fallthrough */ + case EFX_CHANNEL_STATE_POLL | EFX_CHANNEL_STATE_NAPI_REQ: + return false; + default: + break; + } + prev = cmpxchg(&channel->busy_poll_state, old, + EFX_CHANNEL_STATE_NAPI); + if (unlikely(prev != old)) { + /* This is likely to mean we've just entered polling + * state. Go back round to set the REQ bit. + */ + old = prev; + continue; + } + return true; } - spin_unlock_bh(&channel->state_lock); - return rc; } static inline void efx_channel_unlock_napi(struct efx_channel *channel) { - spin_lock_bh(&channel->state_lock); - WARN_ON(channel->state & - (EFX_CHANNEL_STATE_POLL | EFX_CHANNEL_STATE_NAPI_YIELD)); - - channel->state &= EFX_CHANNEL_STATE_DISABLED; - spin_unlock_bh(&channel->state_lock); + /* Make sure write has completed from efx_channel_lock_napi() */ + smp_wmb(); + WRITE_ONCE(channel->busy_poll_state, EFX_CHANNEL_STATE_IDLE); } /* Called from efx_busy_poll(). */ -static inline bool efx_channel_lock_poll(struct efx_channel *channel) +static inline bool efx_channel_try_lock_poll(struct efx_channel *channel) { - bool rc = true; - - spin_lock_bh(&channel->state_lock); - if ((channel->state & EFX_CHANNEL_LOCKED)) { - channel->state |= EFX_CHANNEL_STATE_POLL_YIELD; - rc = false; - } else { - /* preserve yield marks */ - channel->state |= EFX_CHANNEL_STATE_POLL; - } - spin_unlock_bh(&channel->state_lock); - return rc; + return cmpxchg(&channel->busy_poll_state, EFX_CHANNEL_STATE_IDLE, + EFX_CHANNEL_STATE_POLL) == EFX_CHANNEL_STATE_IDLE; } -/* Returns true if NAPI tried to get the channel while it was locked. */ static inline void efx_channel_unlock_poll(struct efx_channel *channel) { - spin_lock_bh(&channel->state_lock); - WARN_ON(channel->state & EFX_CHANNEL_STATE_NAPI); - - /* will reset state to idle, unless channel is disabled */ - channel->state &= EFX_CHANNEL_STATE_DISABLED; - spin_unlock_bh(&channel->state_lock); + clear_bit_unlock(EFX_CHANNEL_STATE_POLL_BIT, &channel->busy_poll_state); } -/* True if a socket is polling, even if it did not get the lock. */ static inline bool efx_channel_busy_polling(struct efx_channel *channel) { - WARN_ON(!(channel->state & EFX_CHANNEL_OWNED)); - return channel->state & EFX_CHANNEL_USER_PEND; + return test_bit(EFX_CHANNEL_STATE_POLL_BIT, &channel->busy_poll_state); } static inline void efx_channel_enable(struct efx_channel *channel) { - spin_lock_bh(&channel->state_lock); - channel->state = EFX_CHANNEL_STATE_IDLE; - spin_unlock_bh(&channel->state_lock); + clear_bit_unlock(EFX_CHANNEL_STATE_DISABLE_BIT, + &channel->busy_poll_state); } -/* False if the channel is currently owned. */ +/* Stop further polling or napi access. + * Returns false if the channel is currently busy polling. + */ static inline bool efx_channel_disable(struct efx_channel *channel) { - bool rc = true; - - spin_lock_bh(&channel->state_lock); - if (channel->state & EFX_CHANNEL_OWNED) - rc = false; - channel->state |= EFX_CHANNEL_STATE_DISABLED; - spin_unlock_bh(&channel->state_lock); - - return rc; + set_bit(EFX_CHANNEL_STATE_DISABLE_BIT, &channel->busy_poll_state); + /* Implicit barrier in efx_channel_busy_polling() */ + return !efx_channel_busy_polling(channel); } #else /* CONFIG_NET_RX_BUSY_POLL */ -static inline void efx_channel_init_lock(struct efx_channel *channel) +static inline void efx_channel_busy_poll_init(struct efx_channel *channel) { } @@ -584,7 +567,7 @@ static inline void efx_channel_unlock_napi(struct efx_channel *channel) { } -static inline bool efx_channel_lock_poll(struct efx_channel *channel) +static inline bool efx_channel_try_lock_poll(struct efx_channel *channel) { return false; }