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[212.8.243.115]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45052a48911sm11193626f8f.11.2026.05.06.02.15.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 May 2026 02:15:44 -0700 (PDT) Message-ID: <967f1cd8cd6e27aaa65d68194487306bc312caa0.camel@redhat.com> Subject: Re: [PATCH 07/13] rv: Simply hybrid automata monitors's clock variables From: Gabriele Monaco To: Nam Cao Cc: Steven Rostedt , Wander Lairson Costa , linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Wed, 06 May 2026 11:15:43 +0200 In-Reply-To: References: Autocrypt: addr=gmonaco@redhat.com; prefer-encrypt=mutual; keydata=mDMEZuK5YxYJKwYBBAHaRw8BAQdAmJ3dM9Sz6/Hodu33Qrf8QH2bNeNbOikqYtxWFLVm0 1a0JEdhYnJpZWxlIE1vbmFjbyA8Z21vbmFjb0BrZXJuZWwub3JnPoiZBBMWCgBBFiEEysoR+AuB3R Zwp6j270psSVh4TfIFAmjKX2MCGwMFCQWjmoAFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgk Q70psSVh4TfIQuAD+JulczTN6l7oJjyroySU55Fbjdvo52xiYYlMjPG7dCTsBAMFI7dSL5zg98I+8 cXY1J7kyNsY6/dcipqBM4RMaxXsOtCRHYWJyaWVsZSBNb25hY28gPGdtb25hY29AcmVkaGF0LmNvb T6InAQTFgoARAIbAwUJBaOagAULCQgHAgIiAgYVCgkICwIEFgIDAQIeBwIXgBYhBMrKEfgLgd0WcK eo9u9KbElYeE3yBQJoymCyAhkBAAoJEO9KbElYeE3yjX4BAJ/ETNnlHn8OjZPT77xGmal9kbT1bC1 7DfrYVISWV2Y1AP9HdAMhWNAvtCtN2S1beYjNybuK6IzWYcFfeOV+OBWRDQ== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.1 (3.60.1-1.fc44) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2026-05-05 at 08:59 +0200, Nam Cao wrote: > Hybrid automata monitors's clock variables have two different > representations: >=20 > =C2=A0 - The invariant representation, which is the timestamp when the in= variant > =C2=A0=C2=A0=C2=A0 expires >=20 > =C2=A0 - The guard representation, which is the timestamp when the clock = is last > =C2=A0=C2=A0=C2=A0 reset >=20 > This dual representation makes the logic quite difficult to follow (well, > at least for me). It also complicates the monitors and the generation too= l, > as it requires conversion back and forth between the representation. >=20 > Simplify by using the clock variables for a single purpose: storing the > time stamp since the clock is last reset. >=20 > This also allows simplifying rvgen, which will be done in a follow-up > commit. >=20 > Signed-off-by: Nam Cao Well, this is roughly what we discussed in [1]. Now, I didn't submit the throttle monitor yet because it depends on unacked tracepoints. In short, this works with the assumption that the expires value you pass to ha_check_invariant() is the same you used to arm the timer. That's true for constant values only (the deadline) but not for something l= ike the runtime. I couldn't think of a way to rearrange that model not to requi= re the runtime left field. Otherwise.. We could read the remaining time in the timer, but we wouldn't = be able to simulate ns precision when using the timer wheel. Now if we really wanted to go down that path, we are using a union to alloc= ate either timer or hrtimer, the latter is larger, so we /could/ add a u64 expi= re_ns field to the ha_monitor struct without needing additional memory. If that doesn't sound too wild to you, I may try and sketch something up to= see if that's viable. Then this patch could go through as is and I would add th= e extension together with the submission of throttle. What do you think? Thanks, Gabriele [1] - https://lore.kernel.org/lkml/0c61c0bbbdc2002efb638dccda1f0a18c51d29df.camel= @redhat.com > --- > =C2=A0include/rv/ha_monitor.h=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 | 60 ++++++---= --------------- > =C2=A0kernel/trace/rv/monitors/nomiss/nomiss.c | 18 +------ > =C2=A0kernel/trace/rv/monitors/stall/stall.c=C2=A0=C2=A0 |=C2=A0 2 +- > =C2=A03 files changed, 17 insertions(+), 63 deletions(-) >=20 > diff --git a/include/rv/ha_monitor.h b/include/rv/ha_monitor.h > index d59507e8cb30..1ce3fd324d2c 100644 > --- a/include/rv/ha_monitor.h > +++ b/include/rv/ha_monitor.h > @@ -253,19 +253,8 @@ static inline void __ha_monitor_timer_callback(struc= t > ha_monitor *ha_mon) > =C2=A0} > =C2=A0 > =C2=A0/* > - * The clock variables have 2 different representations in the env_store= : > - * - The guard representation is the timestamp of the last reset > - * - The invariant representation is the timestamp when the invariant ex= pires > - * As the representations are incompatible, care must be taken when swit= ching > - * between them: the invariant representation can only be used when star= ting > a > - * timer when the previous representation was guard (e.g. no other invar= iant > - * started since the last reset operation). > - * Likewise, switching from invariant to guard representation without a = reset > - * can be done only by subtracting the exact value used to start the > invariant. > - * > - * Reading the environment variable (ha_get_clk) also reflects this > difference > - * any reads in states that have an invariant return the (possibly negat= ive) > - * time since expiration, other reads return the time since last reset. > + * The clock variables store the time epoch - the timestamp when the clo= ck > was last reset. > + * They are read by subtracting the time epoch from the current time. > =C2=A0 */ > =C2=A0 > =C2=A0/* > @@ -279,31 +268,21 @@ static inline void ha_reset_clk_ns(struct ha_monito= r > *ha_mon, enum envs env, u64 > =C2=A0{ > =C2=A0 WRITE_ONCE(ha_mon->env_store[env], time_ns); > =C2=A0} > -static inline void ha_set_invariant_ns(struct ha_monitor *ha_mon, enum e= nvs > env, > - =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 u64 value, u64 time_ns) > -{ > - WRITE_ONCE(ha_mon->env_store[env], time_ns + value); > -} > -static inline bool ha_check_invariant_ns(struct ha_monitor *ha_mon, > - enum envs env, u64 time_ns) > +static inline bool ha_check_invariant_ns(struct ha_monitor *ha_mon, enum= envs > env, > + u64 time_ns, u64 expire_ns) > =C2=A0{ > - return READ_ONCE(ha_mon->env_store[env]) >=3D time_ns; > + return time_ns - READ_ONCE(ha_mon->env_store[env]) <=3D expire_ns; > =C2=A0} > =C2=A0/* > =C2=A0 * ha_invariant_passed_ns - prepare the invariant and return the ti= me since > reset > =C2=A0 */ > -static inline u64 ha_invariant_passed_ns(struct ha_monitor *ha_mon, enum= envs > env, > - =C2=A0=C2=A0 u64 expire, u64 time_ns) > +static inline u64 ha_invariant_passed_ns(struct ha_monitor *ha_mon, enum= envs > env, u64 time_ns) > =C2=A0{ > - u64 passed =3D 0; > - > =C2=A0 if (env < 0 || env >=3D ENV_MAX_STORED) > =C2=A0 return 0; > =C2=A0 if (ha_monitor_env_invalid(ha_mon, env)) > =C2=A0 return 0; > - passed =3D ha_get_env(ha_mon, env, time_ns); > - ha_set_invariant_ns(ha_mon, env, expire - passed, time_ns); > - return passed; > + return ha_get_env(ha_mon, env, time_ns); > =C2=A0} > =C2=A0 > =C2=A0/* > @@ -317,32 +296,21 @@ static inline void ha_reset_clk_jiffy(struct ha_mon= itor > *ha_mon, enum envs env) > =C2=A0{ > =C2=A0 WRITE_ONCE(ha_mon->env_store[env], get_jiffies_64()); > =C2=A0} > -static inline void ha_set_invariant_jiffy(struct ha_monitor *ha_mon, > - =C2=A0 enum envs env, u64 value) > -{ > - WRITE_ONCE(ha_mon->env_store[env], get_jiffies_64() + value); > -} > -static inline bool ha_check_invariant_jiffy(struct ha_monitor *ha_mon, > - =C2=A0=C2=A0=C2=A0 enum envs env, u64 time_ns) > +static inline bool ha_check_invariant_jiffy(struct ha_monitor *ha_mon, e= num > envs env, > + =C2=A0=C2=A0=C2=A0 u64 time_ns, u64 expire_jiffy) > =C2=A0{ > - return time_after64(READ_ONCE(ha_mon->env_store[env]), > get_jiffies_64()); > - > + return time_after64(READ_ONCE(ha_mon->env_store[env]) + expire_jiffy, > get_jiffies_64()); > =C2=A0} > =C2=A0/* > =C2=A0 * ha_invariant_passed_jiffy - prepare the invariant and return the= time > since reset > =C2=A0 */ > -static inline u64 ha_invariant_passed_jiffy(struct ha_monitor *ha_mon, e= num > envs env, > - =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 u64 expire, u64 time_ns) > +static inline u64 ha_invariant_passed_jiffy(struct ha_monitor *ha_mon, e= num > envs env, u64 time_ns) > =C2=A0{ > - u64 passed =3D 0; > - > =C2=A0 if (env < 0 || env >=3D ENV_MAX_STORED) > =C2=A0 return 0; > =C2=A0 if (ha_monitor_env_invalid(ha_mon, env)) > =C2=A0 return 0; > - passed =3D ha_get_env(ha_mon, env, time_ns); > - ha_set_invariant_jiffy(ha_mon, env, expire - passed); > - return passed; > + return ha_get_env(ha_mon, env, time_ns); > =C2=A0} > =C2=A0 > =C2=A0/* > @@ -389,14 +357,14 @@ static inline void ha_setup_timer(struct ha_monitor > *ha_mon) > =C2=A0static inline void ha_start_timer_jiffy(struct ha_monitor *ha_mon, = enum envs > env, > =C2=A0 u64 expire, u64 time_ns) > =C2=A0{ > - u64 passed =3D ha_invariant_passed_jiffy(ha_mon, env, expire, time_ns); > + u64 passed =3D ha_invariant_passed_jiffy(ha_mon, env, time_ns); > =C2=A0 > =C2=A0 mod_timer(&ha_mon->timer, get_jiffies_64() + expire - passed); > =C2=A0} > =C2=A0static inline void ha_start_timer_ns(struct ha_monitor *ha_mon, enu= m envs > env, > =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0 u64 expire, u64 time_ns) > =C2=A0{ > - u64 passed =3D ha_invariant_passed_ns(ha_mon, env, expire, time_ns); > + u64 passed =3D ha_invariant_passed_ns(ha_mon, env, time_ns); > =C2=A0 > =C2=A0 ha_start_timer_jiffy(ha_mon, ENV_MAX_STORED, > =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0 nsecs_to_jiffies(expire - passed + TICK= _NSEC - > 1), time_ns); > diff --git a/kernel/trace/rv/monitors/nomiss/nomiss.c > b/kernel/trace/rv/monitors/nomiss/nomiss.c > index 31f90f3638d8..6b3f93866d56 100644 > --- a/kernel/trace/rv/monitors/nomiss/nomiss.c > +++ b/kernel/trace/rv/monitors/nomiss/nomiss.c > @@ -57,24 +57,12 @@ static inline bool ha_verify_invariants(struct ha_mon= itor > *ha_mon, > =C2=A0 enum states next_state, u64 time_ns) > =C2=A0{ > =C2=A0 if (curr_state =3D=3D ready_nomiss) > - return ha_check_invariant_ns(ha_mon, clk_nomiss, time_ns); > + return ha_check_invariant_ns(ha_mon, clk_nomiss, time_ns, > DEADLINE_NS(ha_mon)); > =C2=A0 else if (curr_state =3D=3D running_nomiss) > - return ha_check_invariant_ns(ha_mon, clk_nomiss, time_ns); > + return ha_check_invariant_ns(ha_mon, clk_nomiss, time_ns, > DEADLINE_NS(ha_mon)); > =C2=A0 return true; > =C2=A0} > =C2=A0 > -static inline void ha_convert_inv_guard(struct ha_monitor *ha_mon, > - enum states curr_state, enum events > event, > - enum states next_state, u64 time_ns) > -{ > - if (curr_state =3D=3D next_state) > - return; > - if (curr_state =3D=3D ready_nomiss) > - ha_inv_to_guard(ha_mon, clk_nomiss, DEADLINE_NS(ha_mon), > time_ns); > - else if (curr_state =3D=3D running_nomiss) > - ha_inv_to_guard(ha_mon, clk_nomiss, DEADLINE_NS(ha_mon), > time_ns); > -} > - > =C2=A0static inline bool ha_verify_guards(struct ha_monitor *ha_mon, > =C2=A0 =C2=A0=C2=A0=C2=A0 enum states curr_state, enum events > event, > =C2=A0 =C2=A0=C2=A0=C2=A0 enum states next_state, u64 time_ns) > @@ -122,8 +110,6 @@ static bool ha_verify_constraint(struct ha_monitor > *ha_mon, > =C2=A0 if (!ha_verify_invariants(ha_mon, curr_state, event, next_state, > time_ns)) > =C2=A0 return false; > =C2=A0 > - ha_convert_inv_guard(ha_mon, curr_state, event, next_state, time_ns); > - > =C2=A0 if (!ha_verify_guards(ha_mon, curr_state, event, next_state, > time_ns)) > =C2=A0 return false; > =C2=A0 > diff --git a/kernel/trace/rv/monitors/stall/stall.c > b/kernel/trace/rv/monitors/stall/stall.c > index 9ccfda6b0e73..1aa65d7e690d 100644 > --- a/kernel/trace/rv/monitors/stall/stall.c > +++ b/kernel/trace/rv/monitors/stall/stall.c > @@ -38,7 +38,7 @@ static inline bool ha_verify_invariants(struct ha_monit= or > *ha_mon, > =C2=A0 enum states next_state, u64 time_ns) > =C2=A0{ > =C2=A0 if (curr_state =3D=3D enqueued_stall) > - return ha_check_invariant_jiffy(ha_mon, clk_stall, time_ns); > + return ha_check_invariant_jiffy(ha_mon, clk_stall, time_ns, > threshold_jiffies); > =C2=A0 return true; > =C2=A0} > =C2=A0